Light orbital angular momentum high-speed detector and method capable of rapidly responding to left and right circular polarization states

Abstract

The invention discloses an optical orbital angular momentum high-speed detector and method for rapid response of left and right circular polarization states. Based on a high-speed polarization modulation technology and an orbital angular momentum detector, information of orbital angular momentum of light is detected at a high speed; compared with a minute-order detection speed based on a traditional detection method, the detection speed of the optical orbital angular momentum is increased to a millisecond order, and meanwhile, the quantum number of the optical orbital angular momentum can be directly distinguished through a circular polarization dependent component of the radial light current extracted by the lock-in amplifier; extra calculation and data processing through a computer are not needed; the photoelastic modulator has a large working wavelength range, so that the method can also be suitable for optical orbital angular momentum detection in a large wavelength range; the method is applied to various optical orbital angular momentum detection application occasions such as infrared imaging, military reconnaissance and focal plane imaging.

Description

Technical Field

[0001] The invention relates to an optical parameter detection technology, and in particular to an optical orbit angular momentum high-speed detector with rapid response to left and right circular polarization states and a detection method thereof. Background Art

[0002] Recent progress in the direct detection of orbital angular momentum (OAM) based on the orbital photogalvanic effect (OPGE) provides an effective method for direct electrical readout of optical OAM on-chip and a path to large-scale integrated focal plane array devices. The OPGE response is driven by the spiral phase gradient of light, and is a photocurrent response generated by the interaction of the spatially uneven light field with the electric quadrupole moment and magnetic dipole moment of the material. The OAM quantum number can be distinguished by the quantized value of the circular polarization-dependent component of the OPGE response. Currently, the OAM-sensitive materials that have been discovered include two categories, one is the second-type Weyl semimetal materials, including WTe2 and TaIrTe4, and the other is multilayer graphene (MLG) materials. Although the introduction of the optical OAM direct photodetector based on MLG has greatly improved the responsivity and signal-to-noise ratio of the OAM detector based on OPGE, this work still has shortcomings in detection speed. This is because the identification of OAM quantum numbers from the photocurrent response requires the extraction of the circular polarization-dependent component of the OPGE response. Experimentally, it is necessary to set a polarization modulation module in front of the detector, continuously switch the left and right circular polarization states of the incident light, measure the photocurrent response under the excitation of the left and right circular polarization light, and calculate the difference between the two to obtain the circular polarization-dependent component. At present, OAM detection based on OPGE uses the same polarization modulation method, that is, a polarizer and a quarter-wave plate are set in front of the detector, and the left and right circular polarization states of the incident light are switched by rotating the quarter-wave plate. This polarization modulation method is called mechanical modulation. At present, due to the modulation speed limit of the mechanical modulation method and the speed limit of the corresponding circular polarization-dependent component extraction method, the operating speed of the OPGE-based OAM detector is at the minute level, which greatly limits its application in many occasions. To improve the OPGE detection speed, the key is to combine the existing high-speed polarization modulation technology, such as electro-optic modulator (EOM) or photoelastic modulator (PEM), to achieve high-speed extraction of the circular polarization-dependent component of the OPGE response. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention proposes a high-speed detector of optical orbit angular momentum with rapid response to left and right circular polarization states and a detection method thereof.

[0004] One object of the present invention is to provide a high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states.

[0005] The high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states of the present invention comprises: a high-speed polarization modulation module, an orbital angular momentum photoelectric detector and an external detection circuit; wherein,

[0006] The high-speed polarization modulation module includes a polarizer with a fixed polarization direction and a photoelastic modulator; the polarizer is placed at the front end of the photoelastic modulator to adjust the initial polarization of the light beam carrying orbital angular momentum entering the photoelastic modulator; the photoelastic modulator includes an optical end and an electrical end, wherein the optical end includes an optical crystal and a piezoelectric transducer located on both sides of the optical crystal, and the electrical end includes an electronic drive circuit and a controller, the piezoelectric transducer is connected to the electronic drive circuit, and the electronic drive circuit is connected to the controller, and the electronic drive circuit applies a sinusoidally varying drive voltage to the piezoelectric transducer at the optical end according to the parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal; the frequency of the drive voltage matches the resonant frequency of the optical crystal, forming a standing wave in the optical crystal, and periodically changing the birefringence of the optical crystal. radiation properties; the light beam carrying orbital angular momentum passes through an optical crystal, and the optical crystal adds a sinusoidally varying phase difference to the light beam carrying orbital angular momentum along two polarization components perpendicular to the optical axis direction, thereby periodically changing the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidally varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator; by adjusting the polarization direction of the polarizer so that the angle between it and the two optical axes of the optical crystal is 45°, and setting the peak value of the phase difference to be non-zero, the polarization state of the light beam carrying orbital angular momentum passing through the optical crystal changes periodically, so that after being modulated by the photoelastic modulator, the light beam carrying orbital angular momentum experiences one left circular polarization state and one right circular polarization state within one working cycle of the photoelastic modulator;

[0007] The orbital angular momentum detector includes a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate is non-conductive, and the detection material is arranged on the upper surface of the substrate; an electrode structure is arranged on the detection material, and the electrode structure includes a first detection electrode, a second detection electrode and a contact electrode; wherein the first and second detection electrodes are shaped as two concentric partial circular rings with different radii, the inner diameter of the first detection electrode is larger than the outer diameter of the second detection electrode, and the first detection electrode is located outside the second detection electrode; the first electrode and the second electrode are respectively connected to the contact electrode, and are connected to an external detection circuit through the contact electrode; a light beam carrying orbital angular momentum is modulated by a photoelastic modulator, vertically incident on the detection material and located between the first and second detection electrodes, and a net current within the plane is generated in the detection material, and the net current has a radial photocurrent component and an angular photocurrent component. ; The radial photocurrent responses stimulated by the left circular polarization state and the right circular polarization state of the polarization state of the light beam carrying orbital angular momentum have a difference, and the difference between the radial photocurrent responses under the excitation of the left and right circularly polarized lights is the circularly polarized dependence component of the radial photocurrent response, wherein, when the quantum number of the orbital angular momentum of the light changes, the size of the circularly polarized dependence component of the radial photocurrent response also changes accordingly, and when the quantum number of the orbital angular momentum of the light reverses its sign, the direction of the circularly polarized dependence component of the radial photocurrent response also reverses; the light beam carrying orbital angular momentum undergoes a left circular polarization state and a right circular polarization state once within one working cycle of the photoelastic modulator, so that the circularly polarized dependence component of the radial photocurrent response undergoes the same periodic change and has the same frequency as the working frequency of the photoelastic modulator; the first and second detection electrodes collect the radial photocurrent response and output it to an external detection circuit;

[0008] The external detection circuit extracts the component of the radial photocurrent response that is at the same frequency as the operating frequency of the photoelastic modulator through the phase-locked amplification technology, and obtains the circularly polarized dependent component of the radial photocurrent response; the information of the orbital angular momentum of light is directly obtained from the circularly polarized dependent component of the radial photocurrent response, thereby realizing the detection of the orbital angular momentum of light with a wide spectral range and fast response at ambient temperature.

[0009] The controller of the photoelastic modulator outputs a parameter signal to the electronic drive circuit. The electronic drive circuit adjusts the peak value of the drive voltage according to the signal of the controller, and then adjusts the peak value of the phase difference to the set parameter. The response is best when the peak value of the phase difference is π / 2. The optical crystal is made of zinc selenide, fused quartz, calcium fluoride or silicon.

[0010] The light beam carrying orbital angular momentum and having circular polarization state is in the shape of a ring, the outer diameter of the light beam is smaller than the inner diameter of the first detection electrode and the inner diameter of the light beam is larger than the outer diameter of the second detection electrode; the optical phase of the light beam carrying orbital angular momentum changes in the azimuth direction and has a spiral phase gradient. The ring-shaped light beam is located between the first detection electrode and the second detection electrode, and the light beam carries an electric field perpendicular to the propagation direction of the light beam and a magnetic field parallel to the propagation direction of the light beam.

[0011] The light beam carrying orbital angular momentum is vertically incident on the detection material, generating an electric field parallel to the plane of the detection material and a magnetic field perpendicular to the plane of the detection material, namely, an in-plane electric field and an out-of-plane magnetic field; the in-plane electric field and the out-of-plane magnetic field jointly cause a spatial imbalance of carriers in the detection material, thereby generating an in-plane net current in the detection material, which has two components perpendicular to and parallel to the spiral phase gradient, namely, a radial photocurrent component and an angular photocurrent component.

[0012] The detection speed of the orbital angular momentum detector is comparable to the integration time of the phase-locked amplifier, and its theoretical upper limit depends on the operating frequency of the photoelastic modulator and the OPGE signal-to-noise ratio of the orbital angular momentum detector. At present, based on the photoelastic modulator and orbital angular momentum detector with an operating frequency of 50kHz, a detection speed of up to 1kHz can be achieved, which is 4 to 5 orders of magnitude greater than the traditional OAM detection method. The operating frequency of the photoelastic modulator refers to the frequency of the driving voltage, which is equal to the resonant frequency of the optical crystal; the resonant frequency of the optical crystal is 20kHz to 100kHz.

[0013] The upper surface of the base is non-conductive. The base comprises a substrate and a non-conductive layer. The non-conductive layer is formed on the upper surface of the lower substrate.

[0014] The detection material of the orbital angular momentum detector is a second-type Weyl semimetal or multilayer graphene; the second-type Weyl semimetal is tungsten ditelluride WTe2 or tantalum iridium telluride TaIrTe4. Multilayer graphene is prepared by arranging multilayer graphene nanosheets on the surface of a substrate, or epitaxially growing multilayer graphene on a substrate, and the number of layers of multilayer graphene is 5 to 50.

[0015] The first detection electrode, the second detection electrode and the contact electrode are made of a single conductive metal layer; or include two layers: a transition metal layer and a conductive metal layer, and a conductive metal layer is formed on the surface of the transition metal layer, wherein the transition metal layer serves to make the conductive metal layer more firmly adhere to the surface of the multilayer graphene. The material of the conductive metal layer is Au, Al or Cu.

[0016] The partial circular rings of the first and second detection electrodes account for the same proportion of the entire circular ring, and the center lines coincide with each other, accounting for 1 / 4 to 3 / 4.

[0017] Contact electrodes are respectively arranged at both ends of the first detection electrode and the second detection electrode, one end of which is used to connect to an external detection circuit, and the other end is used to form symmetrical contact electrodes at both ends, further limiting the current collection range of the first and second detection electrodes and avoiding stray light from affecting the measurement.

[0018] The width of the first and second detection electrodes is 2-6 μm; the distance between the first detection electrode and the second detection electrode is 4-12 μm.

[0019] The external detection circuit includes: a preamplifier, a phase-locked amplifier and a computer; wherein the first and second detection electrodes of the orbital angular momentum detector are respectively connected to the preamplifier; the preamplifier is connected to the photocurrent signal input terminal of the phase-locked amplifier, and the reference signal input terminal of the phase-locked amplifier is simultaneously connected to the electrical terminal of the photoelastic modulator; the output terminal of the phase-locked amplifier is connected to the computer; the radial photocurrent response collected by the first and second detection electrodes is amplified by the preamplifier and input into the phase-locked amplifier, and the circular deviation-dependent component of the radial photocurrent response is directly extracted according to the modulation frequency provided by the electronic driving circuit of the electrical terminal of the photoelastic modulator as a reference signal, and transmitted to the computer, and the computer directly obtains the size and sign of the quantum number of the light orbital angular momentum through the size and direction of the circular deviation-dependent component of the radial photocurrent response.

[0020] Another object of the present invention is to provide a high-speed detection method of optical orbital angular momentum with rapid response to left and right circular polarization states.

[0021] The method for high-speed detection of optical orbital angular momentum with rapid response to left and right circular polarization states of the present invention comprises the following steps:

[0022] 1) Generate periodic left circular polarization state and right circular polarization state:

[0023] a) The electronic drive circuit applies a sinusoidally varying drive voltage to the piezoelectric transducer at the optical end according to the parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal; the frequency of the drive voltage matches the resonant frequency of the optical crystal, a standing wave is formed in the optical crystal, and the birefringence property of the optical crystal is periodically changed;

[0024] b) the light beam carrying orbital angular momentum passes through an optical crystal, and the optical crystal adds a sinusoidally varying phase difference to the light beam carrying orbital angular momentum along two polarization components perpendicular to the optical axis, thereby periodically changing the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidally varying phase difference added by the optical crystal is set by a parameter provided by a controller of the photoelastic modulator;

[0025] c) adjusting the polarization direction of the polarizer so that the angle between it and the two optical axes of the optical crystal is 45°, and setting the peak value of the phase difference to be non-zero, so that the polarization state of the light beam carrying the orbital angular momentum passing through the optical crystal changes periodically, so that after being modulated by the photoelastic modulator, the light beam carrying the orbital angular momentum experiences one left circular polarization state and one right circular polarization state within one working cycle of the photoelastic modulator;

[0026] 2) Collect radial photocurrent response:

[0027] a) a light beam carrying orbital angular momentum is modulated by a photoelastic modulator and vertically incident on a detection material between a first detection electrode and a second detection electrode, thereby generating an in-plane net current in the detection material, wherein the net current has a radial photocurrent component and an angular photocurrent component;

[0028] b) the radial photocurrent responses excited by the left circular polarization state and the right circular polarization state of the polarization state of the light beam carrying orbital angular momentum have a difference, and the difference of the radial photocurrent responses under the excitation of the left and right circularly polarized lights is the circularly biased dependence component of the radial photocurrent response, wherein when the quantum number of the orbital angular momentum of the light changes, the size of the circularly biased dependence component of the radial photocurrent response also changes accordingly, and when the quantum number of the orbital angular momentum of the light reverses its sign, the direction of the circularly biased dependence component of the radial photocurrent response also reverses;

[0029] c) the light beam carrying orbital angular momentum experiences a left circular polarization state and a right circular polarization state in one working cycle of the photoelastic modulator, so that the circular polarization-dependent component of the radial photocurrent response experiences the same periodic change and has the same frequency as the working frequency of the photoelastic modulator;

[0030] d) the first and second detection electrodes collect radial photocurrent responses and output them to an external detection circuit;

[0031] 3) Obtain information on the orbital angular momentum of light:

[0032] a) The external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photocurrent response through the phase-locked amplification technology, and obtains the circular deviation-dependent component of the radial photocurrent response;

[0033] b) The information of the orbital angular momentum of light is directly obtained from the circularly biased component of the radial photocurrent response, thereby realizing the detection of the orbital angular momentum of light with a wide spectral range and fast response at ambient temperature.

[0034] Wherein, in step 1) a), the frequency of the driving voltage is 10 kHz to 10 MHz.

[0035] In step 2) a), the optical phase of the light beam carrying orbital angular momentum that is perpendicularly incident on the detection material changes in the azimuthal direction, and the in-plane electric field and out-of-plane magnetic field with spatial gradient jointly cause spatial imbalance of carriers in the detection material. Based on the two-dimensional linear energy band structure of the detection material, as well as the characteristics of high Fermi velocity and long carrier relaxation time, a strong in-plane net current is generated in the detection material through the significant intra-band motion and inter-band transition of carriers. The in-plane net current has two directional responses perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, namely radial photocurrent response and angular photocurrent response.

[0036] In step 3) a), the external detection circuit extracts the component of the radial photocurrent response that is at the same frequency as the operating frequency of the photoelastic modulator through the phase-locked amplification technology, and obtains the circularly polarized dependent component of the radial photocurrent response: the sinusoidal signal output by the phase-locked amplifier and the circularly polarized dependent component of the radial photocurrent response have a coefficient difference. The circularly polarized dependent component of the radial photocurrent response can be obtained by multiplying the amplitude of the sinusoidal signal output by the phase-locked amplifier by a coefficient.

[0037] In step b) of step 3), the magnitude and sign of the quantum number of the light orbital angular momentum are obtained through the magnitude and direction of the circularly biased dependent component of the radial photocurrent response.

[0038] Advantages of the present invention:

[0039] The present invention is based on high-speed polarization modulation technology and an orbital angular momentum detector to achieve high-speed detection of information on the orbital angular momentum of light. Compared with the detection speed of the order of minutes based on traditional detection methods, the present invention improves the detection speed of the orbital angular momentum of light to the order of milliseconds. At the same time, the quantum number of the orbital angular momentum of light can be directly resolved by the circular polarization-dependent component of the radial photocurrent response extracted by a phase-locked amplifier, without the need for additional calculation and data processing by a computer. Since the photoelastic modulator has a large operating wavelength range, the present invention can also be applied to the detection of the orbital angular momentum of light in a large wavelength range. The present invention is applied to various OAM detection applications, such as infrared imaging, military reconnaissance, and focal plane imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of an embodiment of a high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states of the present invention;

[0041] Figure 2 A schematic diagram of the change of the polarization state of a light beam carrying orbital angular momentum within one working cycle of a photoelastic modulator in one embodiment of a high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states of the present invention;

[0042] Figure 3 A schematic diagram of an embodiment of an orbital angular momentum photoelectric detector of a high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states of the present invention;

[0043] Figure 4 It is a schematic diagram of the test results of the circular polarization dependence component of the radial photocurrent of an embodiment of the optical orbital angular momentum high-speed detector with fast response to left and right circular polarization states of the present invention under the incidence of light beams carrying different orbital angular momentums;

[0044] Figure 5Schematic diagram of the test results of the relationship between the circular polarization-dependent component of the extracted radial photocurrent response and the quantum number of the light orbital angular momentum under the incidence of light beams carrying different orbital angular momentums in one embodiment of the invention's high-speed detector for fast response of left and right circular polarization states of light orbital angular momentum

[0045] Figure 6 The signal-to-noise ratio test results of the circular polarization dependence of the photocurrent response under different lock-in amplifier integration time settings are shown in FIG. 1 , which are for an embodiment of the optical orbital angular momentum high-speed detector with fast response to left and right circular polarization states of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0047] like Figure 1 As shown, the high-speed detector of optical orbital angular momentum with rapid response to left and right circular polarization states of this embodiment comprises: a high-speed polarization modulation module, an orbital angular momentum photoelectric detector and an external detection circuit; wherein the polarizer, the optical end of the photoelastic modulator and the orbital angular momentum detector constitute an optical part; the electrical end of the photoelastic modulator and the external detection circuit constitute an electrical part;

[0048] The high-speed polarization modulation module includes a polarizer with a fixed polarization direction and a photoelastic modulator; the polarizer is placed at the front end of the photoelastic modulator to adjust the initial polarization of a light beam carrying orbital angular momentum entering the photoelastic modulator; the photoelastic modulator includes an optical end and an electrical end, wherein the optical end includes an optical crystal and piezoelectric transducers located on both sides of the optical crystal, the polarizer and the optical crystal are located in the xy plane, and the optical axis is perpendicular to the xy plane, the electrical end includes an electronic drive circuit and a controller, the piezoelectric transducer is connected to the electronic drive circuit, the electronic drive circuit is connected to the controller, the electronic drive circuit applies a sinusoidally varying drive voltage to the piezoelectric transducer at the optical end according to a parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal, a part of the optical crystal is a light-transmitting part, and piezoelectric transducers are respectively arranged on both sides of the other part of the optical crystal, and the parameter signal provided by the controller includes the frequency of the drive voltage and the peak value of the phase difference; such as Figure 2As shown, when the frequency of the driving voltage matches the resonance frequency of the optical crystal, a standing wave is formed in the optical crystal, and the birefringence property of the optical crystal is periodically changed; the light beam carrying orbital angular momentum passes through the optical crystal, and the optical crystal adds a sinusoidally varying phase difference to the light beam carrying orbital angular momentum along two polarization components perpendicular to the optical axis direction, thereby periodically changing the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidally varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator; by adjusting the polarization direction of the polarizer so that the angle between it and the two optical axes of the optical crystal is 45°, and setting the peak value of the phase difference to π / 2, the polarization state of the light beam carrying orbital angular momentum passing through the optical crystal changes periodically, so that after being modulated by the photoelastic modulator, the light beam carrying orbital angular momentum undergoes a left circular polarization state and a right circular polarization state within one working cycle of the photoelastic modulator; Figure 1 In the equation, E represents the electric field and the direction represents the polarization direction of the light beam;

[0049] like Figure 3As shown, the orbital angular momentum detector includes a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate 1 is non-conductive, and a detection material 2 is arranged on the upper surface of the substrate; an electrode structure is arranged on the detection material, and the electrode structure includes a first detection electrode, a second detection electrode and a contact electrode; wherein the shapes of the first and second detection electrodes are respectively two concentric partial circular rings with different radii, the same proportion and overlapping center lines, the partial circular rings of the first and second detection electrodes account for 1 / 2 of the entire circular ring, the inner diameter of the first detection electrode is larger than the outer diameter of the second detection electrode, and the first detection electrode 3 is located outside the second detection electrode 4; the first electrode and the second electrode are respectively connected to the contact electrode 5, and are connected to the contact electrode through the contact electrode An external detection circuit 6; a light beam carrying orbital angular momentum and having a circular polarization state, which is in the shape of a ring, wherein the outer diameter of the light beam is smaller than the inner diameter of the first detection electrode and the inner diameter of the light beam is larger than the outer diameter of the second detection electrode; the optical phase of the light beam carrying orbital angular momentum varies in the azimuthal direction and has a spiral phase gradient; the light beam carries an electric field perpendicular to the propagation direction of the light beam and a magnetic field parallel to the propagation direction of the light beam; the light beam carrying orbital angular momentum is modulated by a photoelastic modulator and vertically incident on the detection material, and the ring-shaped light beam is located between the first detection electrode and the second detection electrode, generating an electric field parallel to the plane of the detection material and a magnetic field perpendicular to the plane of the detection material, namely, an in-plane electric field and an out-of-plane magnetic field; vertically incident on The optical phase of the light beam carrying orbital angular momentum of the detection material changes in the azimuthal direction. The in-plane electric field and out-of-plane magnetic field with spatial gradient jointly cause spatial imbalance of carriers in multilayer graphene. Based on the two-dimensional linear band structure of multilayer graphene, as well as the characteristics of high Fermi velocity and long carrier relaxation time, a strong in-plane net current is generated in multilayer graphene through significant intra-band motion and inter-band transition of carriers. The in-plane net current has two directional responses, perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, namely radial photocurrent response and angular photocurrent response. The radial photocurrent response excited by the left circular polarization state and the right circular polarization state of the polarization state of the light beam carrying orbital angular momentum has a difference, namely, the left The difference of the radial photocurrent response under the excitation of right circularly polarized light is the circularly polarized component of the radial photocurrent response, wherein when the quantum number of the orbital angular momentum of the light changes, the size of the circularly polarized component of the radial photocurrent response also changes accordingly, and when the quantum number of the orbital angular momentum of the light reverses its sign, the direction of the circularly polarized component of the radial photocurrent response also reverses; the light beam carrying the orbital angular momentum undergoes a left circular polarization state and a right circular polarization state within one working cycle of the photoelastic modulator, so that the circularly polarized component of the radial photocurrent response undergoes the same periodic change and has the same frequency as the working frequency of the photoelastic modulator; the first and second detection electrodes collect the radial photocurrent response and output it to an external detection circuit;

[0050] The external detection circuit extracts the component of the radial photocurrent response that is at the same frequency as the operating frequency of the photoelastic modulator through the phase-locked amplification technology, and obtains the circular polarization dependence component of the radial photocurrent response; the information of the light orbital angular momentum is directly obtained from the circular polarization dependence component of the radial photocurrent response, and the size and sign of the quantum number of the light orbital angular momentum are obtained through the size and direction of the circular polarization dependence component of the radial photocurrent response, thereby realizing the detection of light orbital angular momentum information with a wide spectral range and fast response at ambient temperature.

[0051] In this embodiment, the operating frequency of the photoelastic modulator is 50kHz, the peak value of the phase difference is π / 2, and the response is the best; the detection material of the orbital angular momentum detector is multilayer graphene; the substrate includes a highly doped silicon substrate and a 300nm thick non-conductive layer of silicon dioxide SiO2, and the highly doped silicon conductive layer is P-type doped or N-type doped; multilayer graphene is epitaxially grown on the substrate 1, and the thickness of the multilayer graphene 2 is 25nm; the first detection electrode 3, the second detection electrode 4 and the contact electrode 5 include two layers: the lower transition metal layer is Ti with a thickness of 10nm, and the upper conductive metal layer is Au with a thickness of 80nm; the thickness of the epitaxially grown multilayer graphene 2 is 25nm; the partial ring shape of the first and second detection electrodes 4 accounts for 1 / 2 of the entire ring shape; contact electrodes 5 are respectively arranged at both ends of the first detection electrode 3 and the second detection electrode 4, one end of which is used to connect to an external detection circuit, and the other end is used to form a contact electrode 5 symmetrical at both ends, further limiting the current collection range of the first and second detection electrodes 4 to avoid stray light affecting the measurement. The conductive metal layer on the transition metal layer is Au with a thickness of 80 nm.

[0052] Figure 4 The test results of the circular deflection dependence component of the radial photocurrent under the incidence of light beams carrying different orbital angular momentums based on an embodiment of the detection means are given, wherein the orbital angular momentum detector uses multilayer graphene as the detection material. The quantum numbers of the six types of orbital angular momentum of light are +4, +2, +1, -4, -2 and -1 respectively. The test process adopts an on-off test, that is, the light is shielded during the test of 0 to 15 seconds and 35 to 50 seconds, and the light is passed during the test of 15 to 35 seconds. By calculating the response difference between shielding and passing the light, the components from electrical interference in the response are eliminated to obtain the circular deflection dependence component of the radial photocurrent response. The test results show that when the quantum number of the orbital angular momentum of light is positive, the circular deflection dependence component of the radial photocurrent response obtained by the detection means is positive. Conversely, when the quantum number of the orbital angular momentum of light is negative, the circular deflection dependence component of the radial photocurrent response obtained by the detection means is negative. Moreover, the larger the quantum number of the orbital angular momentum of light, the larger the circular deflection dependence component obtained. The test results are consistent with those based on traditional detection methods, verifying that this detection method has the ability to directly detect the orbital angular momentum of light.

[0053] Figure 5 The test results of the relationship between the circular deflection dependence component of the extracted radial photocurrent and the quantum number of the light orbital angular momentum under the incidence of light beams carrying different orbital angular momentum based on an embodiment of the present invention are given. The circular deflection dependence component of the radial photocurrent is proportional to the quantum number of the light orbital angular momentum. The larger the quantum number of the light orbital angular momentum, the larger the circular deflection dependence component; when the quantum number of the light orbital angular momentum reverses its sign, the circular deflection dependence component also reverses its sign. The quantized response of the light orbital angular momentum further verifies the feasibility of the detection scheme. In addition, the light orbital angular momentum detection function and the general light intensity detection function can be performed simultaneously.

[0054] Figure 6 The signal-to-noise ratio test results of the circular deflection dependence component of the radial photocurrent under different phase-locked amplifier integration time settings based on an embodiment of the present invention are given. The quantum numbers of orbital angular momentum carried by the two incident light beams used in the test process are +4 and -4 respectively, and the six phase-locked amplifier integration times used are 300ms, 100ms, 30ms, 10ms, 3ms and 1ms respectively. The test process adopts an on-off test. The test results show that for the same quantum number of light orbital angular momentum and different phase-locked amplifier integration times, the circular deflection dependence component of the radial photocurrent response obtained by the on-off test remains unchanged, and its uncertainty range increases with the decrease of the phase-locked amplifier integration time. The resolution of light orbital angular momentum requires that the circular deflection dependence component of the radial photocurrent response detected under different quantum numbers of light orbital angular momentum has a resolvable difference. Therefore, the test results show that under the existing modulation speed and signal-to-noise ratio, the quantum number resolution of ±4 light orbital angular momentum at a speed of up to 1kHz can be achieved based on the present invention.

[0055] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A high-speed detector of optical orbital angular momentum with fast response to left and right circular polarization states, characterized in that: The high-speed detector of optical orbital angular momentum includes: a high-speed polarization modulation module, an orbital angular momentum photodetector and an external detection circuit; wherein the high-speed polarization modulation module includes a polarizer with a fixed polarization direction and a photoelastic modulator; the polarizer is placed at the front end of the photoelastic modulator to adjust the initial polarization of the light beam carrying orbital angular momentum entering the photoelastic modulator; the photoelastic modulator includes an optical end and an electrical end, wherein the optical end includes an optical crystal and a piezoelectric transducer located on both sides of the optical crystal, the electrical end includes an electronic drive circuit and a controller, the piezoelectric transducer is connected to the electronic drive circuit, the electronic drive circuit is connected to the controller, and the electronic drive circuit applies a sinusoidally varying drive voltage to the piezoelectric transducer at the optical end according to a parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal; the frequency of the drive voltage matches the resonant frequency of the optical crystal , a standing wave is formed in the optical crystal, and the birefringence property of the optical crystal is periodically changed; the light beam carrying orbital angular momentum passes through the optical crystal, and the optical crystal adds a sinusoidally varying phase difference to the light beam carrying orbital angular momentum along two polarization components perpendicular to the optical axis direction, thereby periodically changing the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidally varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator; by adjusting the polarization direction of the polarizer so that the angle between it and the two optical axes of the optical crystal is 45°, and setting the peak value of the phase difference to be non-zero, the polarization state of the light beam carrying orbital angular momentum passing through the optical crystal changes periodically, thereby being modulated by the photoelastic modulator, and within one working cycle of the photoelastic modulator, the light beam carrying orbital angular momentum experiences one left circular polarization state and one right circular polarization state; The orbital angular momentum detector includes a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate is non-conductive, and the detection material is arranged on the upper surface of the substrate; an electrode structure is arranged on the detection material, and the electrode structure includes a first detection electrode, a second detection electrode and a contact electrode; wherein the first and second detection electrodes are shaped as two concentric partial circular rings with different radii, the inner diameter of the first detection electrode is larger than the outer diameter of the second detection electrode, and the first detection electrode is located outside the second detection electrode; the first electrode and the second electrode are respectively connected to the contact electrode, and are connected to an external detection circuit through the contact electrode; a light beam carrying orbital angular momentum is modulated by a photoelastic modulator, vertically incident on the detection material and located between the first and second detection electrodes, generating an in-plane net current in the detection material, and the net current has a radial photocurrent component and an angular photocurrent component. The radial photocurrent response excited by the left circular polarization state and the right circular polarization state of the polarization state of the light beam carrying orbital angular momentum has a difference, and the difference of the radial photocurrent response under the excitation of the left and right circular polarized light is the circularly polarized dependence component of the radial photocurrent response, wherein, when the quantum number of the orbital angular momentum of the light changes, the size of the circularly polarized dependence component of the radial photocurrent response also changes accordingly, and when the quantum number of the orbital angular momentum of the light reverses its sign, the direction of the circularly polarized dependence component of the radial photocurrent response also reverses; the light beam carrying orbital angular momentum undergoes a left circular polarization state and a right circular polarization state once in one working cycle of the photoelastic modulator, so that the circularly polarized dependence component of the radial photocurrent response undergoes the same periodic change and has the same frequency as the working frequency of the photoelastic modulator; the first and second detection electrodes collect the radial photocurrent response and output it to an external detection circuit; The external detection circuit extracts the component of the radial photocurrent response that is at the same frequency as the operating frequency of the photoelastic modulator through the phase-locked amplification technology, and obtains the circular deviation-dependent component of the radial photocurrent response; the information of the light orbital angular momentum is directly obtained from the circular deviation-dependent component of the radial photocurrent response, thereby realizing the detection of light orbital angular momentum information with a wide spectral range and fast response at ambient temperature.

2. The optical orbital angular momentum high-speed detector according to claim 1, characterized in that: The optical crystal is made of zinc selenide, fused quartz, calcium fluoride or silicon.

3. The high-speed optical orbital angular momentum detector according to claim 1, characterized in that: The light beam carrying orbital angular momentum and having a circular polarization state is in a ring shape, the outer diameter of the light beam is smaller than the inner diameter of the first detection electrode and the inner diameter of the light beam is larger than the outer diameter of the second detection electrode; the optical phase of the light beam carrying orbital angular momentum changes in the azimuth direction and has a spiral phase gradient.

4. The optical orbital angular momentum high-speed detector according to claim 1, characterized in that: The detection material of the orbital angular momentum detector is a second-type Weyl semimetal or multilayer graphene.

5. The optical orbital angular momentum high-speed detector according to claim 1, characterized in that: The partial circular shapes of the first and second detection electrodes have the same proportion to the entire circular shape, and their center lines coincide, accounting for 1 / 4 to 3 / 4; the width of the first and second detection electrodes is 2 to 6 μm; the distance between the first detection electrode and the second detection electrode is 4 to 12 μm.

6. The optical orbital angular momentum high-speed detector according to claim 1, characterized in that: The external detection circuit includes: a preamplifier, a phase-locked amplifier and a computer; wherein the first and second detection electrodes of the orbital angular momentum detector are respectively connected to the preamplifier; the preamplifier is connected to the photocurrent signal input terminal of the phase-locked amplifier, and the reference signal input terminal of the phase-locked amplifier is simultaneously connected to the electrical terminal of the photoelastic modulator; the output terminal of the phase-locked amplifier is connected to the computer; the radial photocurrent response collected by the first and second detection electrodes is amplified by the preamplifier and input into the phase-locked amplifier, and the circular deviation-dependent component of the radial photocurrent response is directly extracted according to the modulation frequency provided by the electronic driving circuit of the electrical terminal of the photoelastic modulator as a reference signal, and transmitted to the computer, and the computer directly obtains the size and sign of the quantum number of the light orbital angular momentum through the size and direction of the circular deviation-dependent component of the radial photocurrent response.

7. A detection method of the high-speed detector of optical orbital angular momentum with fast response to left and right circular polarization states as claimed in claim 1, characterized in that: The detection method comprises the following steps: 1) Generate periodic left circular polarization state and right circular polarization state: a) The electronic drive circuit applies a sinusoidally varying drive voltage to the piezoelectric transducer at the optical end according to the parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal; the frequency of the drive voltage matches the resonant frequency of the optical crystal, a standing wave is formed in the optical crystal, and the birefringence property of the optical crystal is periodically changed; b) the light beam carrying orbital angular momentum passes through an optical crystal, and the optical crystal adds a sinusoidally varying phase difference to the light beam carrying orbital angular momentum along two polarization components perpendicular to the optical axis, thereby periodically changing the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidally varying phase difference added by the optical crystal is set by a parameter provided by a controller of the photoelastic modulator; c) adjusting the polarization direction of the polarizer so that the angle between it and the two optical axes of the optical crystal is 45°, and setting the peak value of the phase difference to be non-zero, so that the polarization state of the light beam carrying the orbital angular momentum passing through the optical crystal changes periodically, so that after being modulated by the photoelastic modulator, the light beam carrying the orbital angular momentum experiences one left circular polarization state and one right circular polarization state within one working cycle of the photoelastic modulator; 2) Collect radial photocurrent response: a) a light beam carrying orbital angular momentum is modulated by a photoelastic modulator and vertically incident on a detection material and located between a first detection electrode and a second detection electrode, thereby generating an in-plane net current in the detection material, wherein the net current has a radial photocurrent component and an angular photocurrent component; b) the radial photocurrent responses excited by the left circular polarization state and the right circular polarization state of the polarization state of the light beam carrying orbital angular momentum have a difference, and the difference of the radial photocurrent responses under the excitation of the left and right circularly polarized lights is the circularly biased dependence component of the radial photocurrent response, wherein when the quantum number of the orbital angular momentum of the light changes, the size of the circularly biased dependence component of the radial photocurrent response also changes accordingly, and when the quantum number of the orbital angular momentum of the light reverses its sign, the direction of the circularly biased dependence component of the radial photocurrent response also reverses; c) the light beam carrying orbital angular momentum experiences a left circular polarization state and a right circular polarization state in one working cycle of the photoelastic modulator, so that the circular polarization-dependent component of the radial photocurrent response experiences the same periodic change and has the same frequency as the working frequency of the photoelastic modulator; d) the first and second detection electrodes collect radial photocurrent responses and output them to an external detection circuit; 3) Obtain information on the orbital angular momentum of light: a) The external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photocurrent response through the phase-locked amplification technology, and obtains the circular deviation-dependent component of the radial photocurrent response; b) The information of the orbital angular momentum of light is directly obtained from the circularly biased component of the radial photocurrent response, thereby realizing the detection of the orbital angular momentum of light with a wide spectral range and fast response at ambient temperature.

8. The detection method according to claim 7, characterized in that: In step 1) a), the frequency of the driving voltage is 10 kHz to 10 MHz.

9. The detection method according to claim 7, characterized in that: In step 2) a), the optical phase of the light beam carrying orbital angular momentum vertically incident on the detection material changes in the azimuthal direction, and the in-plane electric field and out-of-plane magnetic field with spatial gradient jointly induce the spatial imbalance of carriers in the detection material, based on the two-dimensional linear band structure of the detection material, and The characteristics of high Fermi velocity and long carrier relaxation time generate a strong in-plane net current in the detection material through the significant intra-band motion and inter-band transition of carriers. The in-plane net current has two directional responses, perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, namely radial photocurrent response and angular photocurrent response.

10. The detection method according to claim 7, characterized in that: In step b) of step 3), the magnitude and sign of the quantum number of the light orbital angular momentum are obtained through the magnitude and direction of the circularly biased dependent component of the radial photocurrent response.

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