Method and apparatus for improving signal-to-noise ratio based on vortex light field demodulation

Abstract

The application discloses a method and device for improving signal-to-noise ratio based on vortex light field demodulation, and specifically comprises the following steps: obtaining a first filtered signal of a vortex light detection signal, wherein the first filtered signal is a signal filtered from a first part of an imaging spot of the vortex light detection signal; the vortex light detection signal has a first spiral modulation signal; obtaining a second modulation signal, specifically comprising the following steps: modulating the first filtered signal, which is to apply a second spiral modulation signal to the first filtered signal, wherein the first spiral modulation signal and the second spiral modulation signal have opposite modulation phases; obtaining a second filtered signal, specifically comprising the following steps: filtering a second part of an imaging spot of the second modulation signal, and analyzing the second filtered signal to obtain a detection signal. According to the method and device, the filtered vortex light field is further demodulated, applied in signal analysis and detection, noise interference is suppressed, and the signal-to-noise ratio is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of signal detection, in particular to a method and device for improving signal-to-noise ratio based on vortex light field demodulation. BACKGROUND

[0002] Coherent light (signal light) and background or multiple scattered incoherent light have essential differences in spatial distribution and phase characteristics. Therefore, the coherence of light provides a new dimension for finally improving the signal-to-noise ratio of detection. Vortex light is a specific form of realization. Vortex beam is an orbital angular momentum beam, and its significant feature is that there is an optical singularity with zero light intensity in the center of the beam, and the singularity has a spiral phase distribution.

[0003] Vortex beams have applications in many fields. For example, in optical tweezers, vortex beams are often used to drive micro-particles to rotate. Since vortex beams carry orbital angular momentum, they can be transmitted to microparticles for mechanical testing of single cells and biomolecules and microfluidic dynamics research. Vortex light interference combined with digital holographic technology can measure the surface topography of an object with high precision. The phase singularity will produce characteristic bifurcation in the interference pattern, thereby realizing nanoscale thickness measurement.

[0004] The patent document with patent application number 202310501136.X discloses a method for improving photoelectric signal detection signal-to-noise ratio based on vortex light. This method is to modulate the mixed signal light and non-signal light through an optical path to form a circular ring-shaped signal light and a circular dot-shaped non-signal light, and to set a ring-shaped diaphragm in the Fourier plane to realize first filtering and thereby improve the signal-to-noise ratio.

[0005] However, in the above-mentioned prior art disclosed scheme, there are still problems that have not been solved: when performing the first filtering, although the incoherent light is focused in the center, part of the incoherent noise will still be crosstalk into the coherent annular channel. Therefore, the above method only filters out the incoherent signal in the center, and does not filter out the incoherent signal in the coherent channel, which is difficult to further suppress the environmental noise, and the incoherent light in the coherent channel will affect the final detection signal-to-noise ratio of the system, causing certain application obstacles for signal demodulation detection in higher precision application fields.

[0006] Therefore, the technical personnel in the field urgently need to propose a method and device for improving signal-to-noise ratio based on vortex light field demodulation. SUMMARY

[0007] In view of one or more of the above defects or improvement needs of the prior art, to overcome the problem of the signal-to-noise ratio of vortex light applied to various fields in the prior art, the present application provides a method and device for improving the signal-to-noise ratio based on vortex light field demodulation. The method and device realized according to the present application will further suppress noise interference and improve the signal-to-noise ratio.

[0008] The above improved technical features can be combined with each other as long as they do not conflict with each other.

[0009] The present application discloses a method for improving the signal-to-noise ratio based on vortex light field demodulation, which comprises the following steps:

[0010] S1: obtaining a first filtered signal of a vortex light detection signal, the first filtered signal being a signal filtered from a first part of an imaging spot of the vortex light detection signal; the vortex light detection signal has a first spiral modulation signal;

[0011] S2: obtaining a second modulation signal, specifically: modulating the first filtered signal, the modulation being applying a second spiral modulation signal to the first filtered signal, the first spiral modulation signal and the second spiral modulation signal having opposite modulation phases;

[0012] S3: obtaining a second filtered signal, specifically: a signal filtered from a second part of an imaging spot of the second modulation signal, and analyzing the second filtered signal to obtain a detection signal.

[0013] Further, the step S2 mainly comprises the following sub-steps:

[0014] S21: pre-processing the first filtered signal, the preprocessing being imaging processing of the first filtered signal with a second imaging light path;

[0015] Before the light path where the first filtered signal is generated, there is also a first imaging light path for imaging the vortex light detection signal;

[0016] The first imaging light path and the second imaging light path have conjugate optical parameters;

[0017] S22: performing modulation on the pre-processed signal; the modulation is that the signal transmitted through the second imaging light path is applied to a third modulator to apply a second spiral modulation signal, and the signal passing through the third modulator is applied to a second amplitude modulation signal;

[0018] S23: filtering the light spot modulated by the step 22; the light path where the filtering is performed has a second aperture diameter, and the light path where the first filtered signal is filtered has a first aperture diameter, the first aperture diameter being smaller than the second aperture diameter.

[0019] Further, in the step S22, the second amplitude modulation signal adjusts the spatial propagation direction of the propagation path of the signal.

[0020] Further, the phase order of the first spiral modulation signal and the second spiral modulation signal is greater than a certain threshold, so that the signal-to-noise ratio of the vortex light field demodulation is improved.

[0021] Further, the first part is the center part of the vortex light detection signal imaging spot, and the second part is the annular part of the imaging spot of the second modulation signal.

[0022] The application further discloses a device for improving signal-to-noise ratio based on vortex light field demodulation, which comprises:

[0023] The first vortex light signal demodulation device comprises:

[0024] The first imaging light path is used for beam-reducing imaging of the vortex light detection signal carrying the measurement signal;

[0025] The first diaphragm is used for filtering out the first filtered signal from the first part of the vortex light detection signal imaging spot after beam-reducing imaging.

[0026] The second vortex light signal demodulation device is used for receiving the first filtered signal transmitted by the first vortex light signal demodulation device, and comprises:

[0027] The phase modulator is used for applying a second spiral modulation signal to the first filtered signal to obtain a second modulation signal, wherein the vortex light detection signal carrying the measurement signal has a first spiral modulation signal, and the first spiral modulation signal and the second spiral modulation signal have opposite modulation phases.

[0028] The second diaphragm is used for filtering out a second filtered signal from the second part of the imaging spot of the second modulation signal.

[0029] The first part is the center part of the vortex light detection signal imaging spot after beam-reducing imaging, and the second part is the annular part of the imaging spot of the second modulation signal.

[0030] Further, the second vortex light signal demodulation device comprises a second imaging light path, and the second imaging light path is used for imaging the second modulation signal to generate an imaging spot.

[0031] The first imaging light path and the second imaging light path have conjugate optical parameters.

[0032] Further, the diameter of the first diaphragm is smaller than the diameter of the second diaphragm.

[0033] Further, the phase order of the first spiral modulation signal and the second spiral modulation signal are both greater than a certain threshold, so that the signal-to-noise ratio of the vortex light field demodulation in the demodulation light path is improved.

[0034] Further, the first light barrier is a ring-shaped light barrier for filtering out the center part, and the second light barrier is a center through-hole light barrier for filtering out the ring-shaped part.

[0035] Overall, compared with the prior art, the above technical solutions conceived by the present application have the beneficial effects including:

[0036] The present application proposes that, in the vortex light signal processing, after the first level filtering of the vortex light detection signal, the vortex light detection signal is subjected to second level demodulation filtering, and the signal loaded with the first spiral phase is subjected to the second level modulation and demodulation associated with the first spiral phase, so that the stray light / environmental light signal of the light ring part in the first level demodulation can be further filtered out, and the signal detection signal-to-noise ratio is further improved.

[0037] The present application further proposes that, in the vortex light signal processing device, a spatial modulation device is arranged on the light path after the first level demodulation, the spatial modulation device is used to arrange the second level light path in space, the light path after the spatial modulation device is further adjusted and arranged as the second level modulation and demodulation light path, so that the device can be more conveniently integrated in the application system and the signal processing of the second level different from the first level modulation, and then the imaging is performed after the filtering through the second light barrier, so that the signal detection signal-to-noise ratio is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative labor.

[0039] Figure 1 is a flow framework diagram of the method for improving signal-to-noise ratio based on vortex light field demodulation according to the present application;

[0040] Figure 2 is a flow framework diagram of one step S2 of the method for improving signal-to-noise ratio based on vortex light field demodulation according to the present application;

[0041] Figure 3 is a vortex light-based secondary spatial filtering method flow of the vortex light-based method according to the present application;

[0042] Figure 4 is a vortex light-based secondary spatial filtering device model diagram based on vortex light according to an embodiment of the present application;

[0043] Figure 5 is an application of a vortex light-based secondary spatial filtering device diagram based on vortex light according to an embodiment of the present application in a laser radar detection system;

[0044] FIG. 6(a) is a light intensity distribution diagram of an initial input Gaussian beam according to an embodiment of the present application;

[0045] FIG. 6(b) is a light intensity distribution diagram of an initial input incoherent light according to an embodiment of the present application;

[0046] FIG. 7(a) is a spiral phase distribution diagram of a first spatial light modulator according to an embodiment of the present application when the topological charge number l = 32;

[0047] FIG. 7(b) is a spiral phase distribution diagram of a second spatial light modulator according to an embodiment of the present application when the topological charge number l = 32;

[0048] FIG. 8(a) is a light intensity distribution diagram of a front surface of a first spatial light modulator according to an embodiment of the present application when the aperture diameter is 7.5 mm and the topological charge number l = 32;

[0049] FIG. 8(b) is a phase distribution diagram of the front surface of the first spatial light modulator according to an embodiment of the present application;

[0050] FIG. 9(a) is a light intensity distribution diagram of a vortex beam according to an embodiment of the present application when the topological charge number is 32 and the lens focal length is 100 mm;

[0051] FIG. 9(b) is a phase distribution diagram of the vortex beam according to an embodiment of the present application when the topological charge number is 32 and the lens focal length is 100 mm;

[0052] FIG. 10(a) is a light intensity distribution diagram of a fourth lens according to an embodiment of the present application when the topological charge number is 32 and the lens focal length is 100 mm;

[0053] FIG. 10(b) is a phase distribution diagram of the fourth lens according to an embodiment of the present application when the topological charge number is 32 and the lens focal length is 100 mm;

[0054] FIG. 11(a) is a light intensity distribution diagram of the fourth lens according to an embodiment of the present application when the topological charge number is 32, the lens focal length is 100 mm, and the second aperture diameter is 0.5 mm;

[0055] FIG. 11(b) is a phase distribution diagram of the fourth lens according to an embodiment of the present application when the topological charge number is 32, the lens focal length is 100 mm, and the second aperture diameter is 0.5 mm;

[0056] Fig. 12(a) is a light intensity distribution diagram of the fifth lens in the embodiment of the present application, with a focal length of 100 mm and a third aperture diameter of 0.5 mm;

[0057] Fig. 12(b) is a phase distribution diagram of the fifth lens in the embodiment of the present application, with a focal length of 100 mm and a third aperture diameter of 0.5 mm;

[0058] Fig. 13(a) is a total light intensity distribution diagram of coherent light and incoherent light at the focal plane of the first lens in the embodiment of the present application;

[0059] Fig. 13(b) is a light intensity distribution function diagram derived from the total light intensity distribution of coherent light and incoherent light at the focal plane of the first lens in the embodiment of the present application;

[0060] Fig. 13(c) is a signal-to-noise ratio and inner diameter-outer diameter distribution diagram derived from the total light intensity distribution of coherent light and incoherent light at the focal plane of the first lens in the embodiment of the present application. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0062] For example, in one of the applications of signal detection using vortex light, a laser radar realizes target detection, ranging, imaging and other functions by emitting laser light and then receiving the echo signal. However, in actual environment, especially under strong light conditions or complex atmospheric background, environmental background light (sunlight) and scattered noise often reduce the signal-to-noise ratio of the laser radar, resulting in shortened detection distance, decreased target resolution, and even lost weak echo signals.

[0063] A commonly used method is to load a spiral phase on a spatial light modulator. When coherent light passes through the spiral phase, a clear ring-shaped intensity distribution is formed on the image plane through the lens, while incoherent light still forms an Airy disk on the image plane due to random phase.

[0064] In order to further improve the signal-to-noise ratio of detection, suppressing background light and multiple scattering light becomes an important target to improve the signal-to-noise ratio, and in the prior art, distance gating, narrowband filtering, polarization screening and small field of view are usually used. However, those background light and multiple scattering light which just fall within the gating distance range, are located in the passband of the filter, have the same polarization state as the signal, and also enter the selected field of view will also be filtered out, and these technologies cannot effectively distinguish the signal light and remove the background light. The environmental background light (sunlight) will suppress the signal-to-noise ratio of the laser radar detection in the process of laser radar detection. The spatial separation of coherent light and incoherent light can be realized by using the coherence. The received mixed coherent light and incoherent light are modulated by a spatial light modulator (only coherent light is modulated), and then focused by a lens to realize the spatial separation of the two. The present application proposes a secondary spatial filtering mechanism based on vortex light, which can further filter to improve the signal-to-noise ratio. The vortex light applied in the present application: a beam with an optical singularity with zero light intensity at the center.

[0065] The present application provides a method for improving the signal-to-noise ratio based on vortex light field demodulation, which comprises the following steps:

[0066] S1: obtaining a first filtered signal of the vortex light detection signal, the first filtered signal being a signal filtered from a first part of the vortex light detection signal imaging spot; the vortex light detection signal has a first spiral modulation signal;

[0067] The vortex light detection signal in the present application is a vortex light detection signal after the first spiral modulation signal modulation of the signal to be detected;

[0068] The detection signal is a light signal carrying the information of the object to be detected in the original signal of the probe light, so that the original signal of the probe light can be demodulated and restored to obtain the information of the object to be detected.

[0069] The first filtered signal in the present application is a part that continues to transmit in the optical path after being processed by the optical element arranged in the optical path during the transmission process in the optical path. Generally, the optical element for processing the imaging spot includes an optical diaphragm. Since the vortex light forms a dark singularity phase collapse in the center and a light ring around the periphery in imaging, the corresponding part is filtered out by the diaphragm for further processing in the subsequent optical path, so that the imaging spot is included in the first part in terms of the area of the receiving surface. Accordingly, in one embodiment, the diaphragm is arranged on the receiving surface to filter out the first part and only keep the signal of the light ring.

[0070] S2: obtaining a second modulated signal, specifically, modulating the first filtered signal, the modulation being applying a second spiral modulation signal to the first filtered signal, the first spiral modulation signal and the second spiral modulation signal having opposite modulation phases;

[0071] The phase modulation method is a modulation means known to those skilled in the art for adapting the optical path selection.

[0072] The step S2 mainly includes the following sub-steps:

[0073] S21: pre-processing the first filtered signal, the pre-processing being imaging processing the first filtered signal with a second imaging optical path;

[0074] Before the optical path of the first filtered signal, there is also a first imaging optical path for imaging the vortex light detection signal;

[0075] The first imaging optical path and the second imaging optical path have conjugate optical parameters;

[0076] In this step of the application, a high degree of restoration of the signal is ensured, and the vortex light signal carrying the detection signal is clearly imaged;

[0077] S22: modulating the pre-processed signal; the modulation being transmitting the signal through the second imaging optical path to a third modulator to apply a second spiral modulation signal, and the signal passing through the third modulator being applied with a second amplitude modulation signal;

[0078] In this step of the application, the first demodulated spiral signal is further applied with a second spiral modulation signal, and the optical path is changed on the spatial optical path, which makes the packaging of the device and the optical path more convenient in the application scenario of the laser radar.

[0079] S23: filtering out the light spot modulated in step 22; the filtering-out optical path has a second diaphragm diameter, and the filtering-out optical path of the first filtered signal has a first diaphragm diameter, the first diaphragm diameter being smaller than the second diaphragm diameter.

[0080] In the specific embodiment of the application, in the outdoor application scenario of the laser radar, the full-spectrum light signal noise containing sunlight is formed into a light spot with concentrated brightness at the center of the vortex light ring image, which is the part that needs to be filtered out. In the imaging, a larger optical coefficient is needed to reduce the light spot image size. Therefore, the first diaphragm diameter is smaller than the diaphragm diameter in the second modulation and demodulation optical path.

[0081] S3: obtaining a second filtered signal, specifically, filtering out the second part of the imaging light spot of the second modulated signal, and analyzing the second filtered signal to obtain the detection signal.

[0082] The optical parameters in one of the embodiments of the present application are expressed as shown in the following table:

[0083] Table 1 Optical path parameters for improving signal-to-noise ratio of photoelectric signal detection based on vortex light field modulation and demodulation

[0084]

[0085] The method flow of the present application for improving signal-to-noise ratio of photoelectric signal detection based on vortex light field modulation and demodulation, in another specific embodiment, as shown in Figure 3 , mainly includes the following steps:

[0086] STEP1, passing the received echo light beam through the first aperture and the spatial light modulator, and adding a spiral phase to obtain the light field distribution on the rear surface of the first spatial light modulator;

[0087] STEP2, the light field distribution on the rear surface of the first spatial light modulator is Fourier transformed by the third lens to form a ring-shaped light intensity distribution of vortex light on the image plane of the third lens;

[0088] STEP3, determining the inner diameter and the outer diameter, setting the second aperture on the image plane of the third lens to remove the non-coherent part of the vortex light, playing a single filtering role, obtaining the light field distribution after removing the central non-coherent part, and calculating the signal-to-noise ratio of single filtering;

[0089] STEP4, the light field distribution after removing the central non-coherent part passes through the fourth lens, the second spatial light modulator, and the third aperture, and adds a spiral phase opposite to the first spatial light modulator, thereby eliminating the original spiral phase distribution, realizing the demodulation of the vortex light, and obtaining the light field distribution on the rear surface of the second spatial light modulator;

[0090] STEP5, finally, the light field distribution on the rear surface of the second spatial light modulator is focused to the final image plane by the fifth lens to obtain the light field distribution on the final image plane. The coherent light changes from the initially modulated vortex light ring-shaped distribution to the finally focused Gaussian light distribution in the center, and then the non-coherent light in the coherent channel is filtered out by secondary filtering, and the signal-to-noise ratio after secondary filtering is calculated.

[0091] Further, specifically, in each specific modulation and demodulation optical path setting, it includes:

[0092] STEP1, passing the received echo light beam through the first aperture Aperture1 (generally referred to as an optical function of an aperture, and those skilled in the art can know that the optical function of the aperture can be expressed according to the relationship between the entrance pupil and the exit pupil and the aperture angle) and the third spatial light modulator, and adding a spiral phase the third spatial light modulator rear surface light field distribution .

[0093] wherein the topological charge of the light beam is 32 in one specific embodiment.

[0094] wherein the light field expression through the above optical path is as follows:

[0095] .

[0096] .

[0097] .

[0098] STEP2、third spatial light modulator rear surface light field distribution Fourier transform through the third lens, forming a vortex light annular intensity distribution in the image plane of the third lens ,

[0099] .

[0100] STEP3、determine the inner diameter and the outer diameter of the annular aperture, set the second aperture Aperture2 in the image plane of the third lens, preferably an annular aperture, to remove the incoherent part of the vortex light, play a single filtering role, get the light field distribution removing the central incoherent part , and calculate the signal-to-noise ratio SNR1 of single filtering.

[0101] .

[0102] .

[0103] STEP4、light field distribution removing the central incoherent part Through the fourth lens, the second spatial light modulator and the third aperture Aperture3, the smaller the diameter of the third aperture, the better the effect of the final Gaussian light recovery, but cannot be less than the inner diameter , and additional spiral phase opposite to the first spatial light modulator , so as to eliminate the original spiral phase distribution, realize the demodulation of the vortex light, get the light field distribution after the second spatial light modulator rear surface .

[0104] .

[0105] .

[0106] .

[0107] STEP5, the light field distribution of the last surface of the second spatial light modulator focusing to the final image plane through the fifth lens, and obtaining the light field distribution of the final image plane .

[0108] The coherent light changes from the initial modulated vortex light annular distribution to the final focused Gaussian light distribution in the center, and the non-coherent light in the coherent channel is filtered out through the secondary filtering, and the signal-to-noise ratio SNR2 through the secondary filtering is calculated.

[0109] .

[0110] .

[0111] Further, if the order of the additional spiral phase of the spatial light modulator is increased, the focal length of the optical device on the corresponding optical path is unchanged, thereby achieving the technical effect of improving the signal-to-noise ratio.

[0112] According to one of the devices for improving the signal-to-noise ratio of the optoelectronic signal detection based on vortex light field modulation and demodulation according to the present application, as shown in Figures 4-5 , the coherent light and the non-coherent light received by the laser radar are first subjected to an additional spiral phase through the first spatial light modulator, so that the coherent light becomes an annular light intensity distribution, and the non-coherent light becomes an Airy spot in the center, so that it is subjected to a first spatial filtering in the image plane of the third lens; then, after demodulation by the second spatial light modulator, the annular light intensity distribution of the coherent light is restored to a Gaussian light intensity distribution again, so that it is subjected to a second filtering in the image plane of the fifth lens. The first lens and the second lens constitute a telescope system for beam shrinking.

[0113] Figure 4 is a light path structure diagram of the device for improving the signal-to-noise ratio of the optoelectronic signal detection based on vortex light field modulation and demodulation, in Figure 4 , the coherent light and the non-coherent light are subjected to optical processing by Lens1 and Lens2, pass through the first aperture (Aperture1), reach the spatial light modulator 1 (SLM1), are filtered out by the first stage of the second aperture (Aperture2), reach the spatial light modulator 2 (SLM2), pass through the third aperture (Aperture3), and finally reach the imaging plane for analysis, which can significantly improve the signal-to-noise ratio.

[0114] Figure 5 is a specific application of the light path structure of the device for improving the signal-to-noise ratio of the optoelectronic signal detection based on vortex light field modulation and demodulation in one of the laser radar detection systems.

[0115] In addition to the superposition of the relevant light and the non-relevant light, the present application comprises:

[0116] The first vortex light signal demodulation device comprises:

[0117] The first imaging light path is used for beam-reducing imaging of the vortex light detection signal carrying the measurement signal;

[0118] The second diaphragm is used for filtering out a first part of the imaging spot of the vortex light detection signal after the beam-reducing imaging to generate a first filtered signal;

[0119] The second vortex light signal demodulation device is used for receiving the first filtered signal transmitted by the first vortex light signal demodulation device, and the second vortex light signal demodulation device comprises:

[0120] The phase modulator is used for applying a second spiral modulation signal to the first filtered signal to obtain a second modulation signal, and the vortex light detection signal carrying the measurement signal has a first spiral modulation signal, and the first spiral modulation signal and the second spiral modulation signal have opposite modulation phases;

[0121] The third diaphragm is used for filtering out a second part of the imaging spot of the second modulation signal to generate a second filtered signal;

[0122] The first part is a central part of the imaging spot of the vortex light detection signal after the beam-reducing imaging, and the second part is an annular part of the imaging spot of the second modulation signal.

[0123] As shown in Figure 5 The device is applied to a vortex light analysis light path for measuring a laser radar signal, and comprises:

[0124] The laser is used for generating coherent signal light;

[0125] The mirror is used for changing the light path;

[0126] The beam expander is used for expanding the laser beam;

[0127] The halogen lamp is used for generating a non-coherent light source;

[0128] The collimator is used for collimating the non-coherent light source;

[0129] The beam combiner is used for combining the coherent light and the non-coherent light into one beam;

[0130] The lens group is used for beam-reducing and imaging the combined light;

[0131] The spatial light modulator is used for modulating and demodulating the additional spiral phase, and comprises a spatial light modulator 1 and a spatial light modulator 2;

[0132] A beam profiler for analyzing the spatial distribution of coherent and incoherent light.

[0133] According to the above technical solution, the lens group comprises a first lens, a first diaphragm, a second lens, a second diaphragm, a third lens and a third diaphragm in sequence, that is, Figure 5 As shown in the figure, the diaphragm 1, the diaphragm 2, the diaphragm 3, the lens 1, the lens 2 and the lens 3, and the second diaphragm (the diaphragm 2) are arranged between the lens 1 and the lens 2.

[0134] The performance index of the second spatial light modulator should be consistent with that of the first one, and the X10468 series LCOS-SLM can also be used.

[0135] Usage: reflective phase modulation element;

[0136] Damage and power bearing capacity: the X10468 series SLM may be damaged by heat, photochemistry or surface abrasion under high light power or improper wavelength. The absorption coefficient of liquid crystal increases in the UV band (<350 nm), which can destroy the LC molecules, and the readout light with a wavelength less than 350 nm should be avoided. In order to ensure the linearity of phase modulation and the safety of the device, it is recommended to control the incident angle θ within 10° and use a collimated beam.

[0137] The X10468 series also supports at least 10-bit phase modulation accuracy, and the response speed can reach 10 Hz-60 Hz.

[0138] Firstly, the light generated by the laser passes through the beam expander for beam expansion, at the same time, a halogen lamp is set as a non-coherent light source, the light generated by the halogen lamp passes through the collimator for collimation, and then the coherent light and the non-coherent light pass through the beam combiner to form a mixed light, after that, the mixed light passes through the first diaphragm and then passes through the first spatial light modulator for modulation, after the modulation, the reflected coherent light forms a vortex light on the back focal plane of the first lens, and the non-coherent light forms an Airy disk in the center, then the non-coherent light in the center is filtered out through the second diaphragm, the filtered mixed light passes through the second lens, and then passes through the second spatial light modulator for demodulation to restore a Gaussian light spot, after passing through the reflector, the mixed light passes through the third diaphragm and then passes through the third lens to focus on the back focal plane to restore the original Gaussian light spot, and the beam profiler is used to analyze the distribution at this time.

[0139] Figures 6 (a) and (b) are the input light intensity distribution diagrams of the coherent light and the non-coherent light in the simulation process, in one specific embodiment, the non-coherent light accounts for 30% of the coherent light, so the influence of the ambient light / noise light accounts for a large proportion.

[0140] Further, by adding the spiral phase pattern of Fig. 7(a) on the first spatial light modulator, the light intensity distribution pattern and the spiral phase distribution pattern of Figs. 8(a) and 8(b) are obtained, and the vortex light intensity distribution and the phase distribution of Figs. 9(a) and 9(b) are generated in the image plane of the third lens.

[0141] Further, since the fourth lens and the third lens have the same focal length, a typical 4f system is formed, and according to the characteristics of the 4f system, the light intensity distribution passing through the fourth lens and the light intensity distribution on the front surface of the third lens should be the same, as shown in Figs. 10(a) and 10(b).

[0142] By adding the spiral phase pattern of Fig. 7(b) on the second spatial light modulator, demodulation is performed, and the light intensity distribution pattern and the phase distribution pattern of Figs. 11(a) and 11(b) are obtained, and it is obvious that the uniform phase distribution of the Gaussian light has been restored at this time.

[0143] Further, the light intensity distribution on the rear surface of the second spatial light modulator is focused by the fifth lens, and simulation shows that Figs. 12(a) and 12(b) are the light intensity distribution pattern and the phase distribution pattern of the finally restored coherent light.

[0144] Further, the signal-to-noise ratio of single filtering is calculated by Fig. 13(a), the optimal inner diameter and outer diameter are first determined, the coherent channel and the incoherent channel are determined through the inner diameter and the outer diameter, and then the signal-to-noise ratio is calculated, and the determined inner and outer diameters and the calculated signal-to-noise ratio are shown in Figs. 13(b) and 13(c).

[0145] Further, the signal-to-noise ratio of double filtering is calculated by Fig. 12(a), and the coherent channel at this time is opposite to that of Fig. 13(a), and is concentrated in the middle position at this time.

[0146] Through calculation, the signal-to-noise ratio of double filtering is improved by about 40.34% compared with single filtering, from 6.92 to 9.712.

[0147] The application also discloses a computer program product, comprising a computer program, wherein the computer program is executed by a processor to realize the above method.

[0148] The content described in the specification is only an example of the application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace, as long as the content of the specification is not deviated or the scope defined by the claims is exceeded, which should belong to the protection scope of the application.

Claims

1. A method for improving the signal-to-noise ratio based on vortex optical field demodulation, characterized in that, The method includes the following steps: S1: Obtain the first filtered signal of the vortex light detection signal, wherein the first filtered signal is the signal after filtering out the first part of the imaging spot of the vortex light detection signal; the vortex light detection signal has a first spiral modulation signal; S2: Obtain the second modulation signal, specifically: modulate the first filtered signal, wherein the modulation is to apply a second spiral modulation signal to the first filtered signal, and the first spiral modulation signal and the second spiral modulation signal have opposite modulation phases; S3: Obtain the second filtered signal, specifically: filter out the second part of the imaging spot of the second modulation signal, and analyze the second filtered signal to obtain the detection signal.

2. The method for improving the signal-to-noise ratio based on vortex optical field demodulation as described in claim 1, characterized in that, Step S2 mainly includes the following sub-steps: S21: Preprocess the first filtered signal, wherein the preprocessing is to perform imaging processing on the first filtered signal using the second imaging optical path; Before the optical path that generates the first filtered signal, there is also a first imaging optical path that images the vortex light detection signal; The first imaging optical path and the second imaging optical path have conjugate optical parameters; S22: Modulate the preprocessed signal; The modulation is that the signal transmitted through the second imaging optical path is sent to the third modulator to apply a second spiral modulation signal, and the signal passing through the third modulator is applied with a second amplitude modulation signal; S23: Filter out the light spot modulated in step 22; the optical path for filtering has a second aperture diameter, and the optical path for filtering the first filtered signal has a first aperture diameter, the first aperture diameter being smaller than the second aperture diameter.

3. The method for improving the signal-to-noise ratio based on vortex optical field demodulation as described in claim 2, characterized in that, In step S22, the second amplitude modulation signal adjusts the spatial propagation direction of the signal propagation path.

4. The method for improving the signal-to-noise ratio based on vortex optical field demodulation as described in claim 3, characterized in that, The phase order of the first spiral modulation signal and the second spiral modulation signal is greater than a certain threshold, thereby improving the signal-to-noise ratio of the vortex optical field demodulation.

5. The method for improving the signal-to-noise ratio based on vortex optical field demodulation as described in claim 2, characterized in that, The first part is the central part of the imaging spot of the vortex light detection signal, and the second part is the annular part of the imaging spot of the second modulation signal.

6. A device for improving the signal-to-noise ratio based on vortex optical field demodulation, characterized in that, The device includes: First vortex optical signal demodulation device: The first imaging optical path is used for beam-contraction imaging of the vortex light detection signal carrying the measurement signal; The first aperture is used to filter out a first part of the imaging spot of the vortex light detection signal after beam shrinking imaging to generate a first filtered signal. A second vortex optical signal demodulation device is used to receive a first filtered signal transmitted by the first vortex optical signal demodulation device. The second vortex optical signal demodulation device includes: A phase modulator is used to apply a second spiral modulation signal to the first filtered signal to obtain a second modulation signal. The vortex optical detection signal carrying the measurement signal has a first spiral modulation signal, and the first spiral modulation signal and the second spiral modulation signal have opposite modulation phases. The second aperture is used to filter out the second part of the imaging spot of the second modulation signal to generate a second filtered signal; The first part is the central part of the imaging spot of the vortex light detection signal after beam contraction imaging, and the second part is the annular part of the imaging spot of the second modulation signal.

7. The apparatus for improving signal-to-noise ratio based on vortex optical field demodulation as described in claim 6, characterized in that, The second vortex optical signal demodulation device includes a second imaging optical path, which is used to image the second modulation signal to generate an imaging spot; The first imaging optical path and the second imaging optical path have conjugate optical parameters.

8. The apparatus for improving signal-to-noise ratio based on vortex optical field demodulation as described in claim 7, characterized in that, The diameter of the first aperture is smaller than the diameter of the second aperture.

9. The apparatus for improving signal-to-noise ratio based on vortex optical field demodulation as described in claim 6, characterized in that, The phase order of both the first spiral modulation signal and the second spiral modulation signal is greater than a certain threshold, thereby improving the signal-to-noise ratio of the vortex optical field demodulation in the demodulation optical path.

10. The apparatus for improving signal-to-noise ratio based on vortex optical field demodulation as described in claim 8, characterized in that, The first aperture is an annular aperture used to filter out the central portion, and the second aperture is a central through-hole aperture used to filter out the annular portion.

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