High-speed detector and method for optical orbital angular momentum with fast response of left and right circular polarization states

Abstract

The application discloses a kind of left and right circular polarization state fast response's optical orbital angular momentum high-speed detector and method.The present application is based on high-speed polarization modulation technology and orbital angular momentum detector, realize the information of high-speed detection light orbital angular momentum;Compared with the detection speed of minute order based on traditional detection method, the present application will light orbital angular momentum The detection speed of momentum is promoted to millisecond order, while the number of quantum of light orbital angular momentum can be directly distinguished by the circular polarization dependent component of radial photocurrent extracted by phase-locked amplifier, without additional calculation and data processing by computer;Since photoelastic modulator has a large wavelength range, the present application can also be applied to light orbital angular momentum detection in a larger wavelength range;The present application is applied to various light orbital angular momentum detection application occasions, such as infrared imaging, military investigation and focal plane imaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the optical parametric detection technology, and in particular to a kind of left and right circular polarization state fast response light orbital angular momentum high-speed detector and its detection method. BACKGROUND

[0002] The recent progress in the direct detection of light orbital angular momentum (OAM) based on the orbital photogalvanic effect (OPGE) provides an effective method for on-chip direct electrical readout of light OAM and a way for large-scale integrated focal plane array devices. The OPGE response is driven by the spiral phase gradient of light, and the photoelectric current response is generated by the interaction of 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. The OAM sensitive materials found so far include two categories. One is the second type of Weyl semimetal material, including WTe2 and TaIrTe4. The other is multilayer graphene (MLG) material. Although the proposal of the light OAM direct photodetector based on MLG greatly improves the responsivity and signal-to-noise ratio of the OAM detector based on OPGE, there is still a deficiency in the detection speed. This is because the OAM quantum number needs to be identified from the photoelectric current response by extracting the circular polarization dependent component of the OPGE response. Experimentally, a polarization modulation module needs to be set in front of the detector to switch the left and right circular polarization states of the incident light constantly, measure the photoelectric current response under the excitation of left and right circularly polarized light respectively, and calculate the difference between the two to obtain the circular polarization dependent component. At present, the same polarization modulation method is used for OAM detection based on OPGE, i.e. 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, limited by the modulation speed of the mechanical modulation method and the speed of the corresponding circular polarization dependent component extraction method, the operation speed of the OAM detector based on OPGE is in the order of minutes, which greatly limits its application in many occasions. To improve the OPGE detection speed, the key is to combine existing high-speed polarization modulation technologies such as electro-optic modulator (EOM) or photoelastic modulator (PEM) to realize high-speed extraction of the circular polarization dependent component of the OPGE response. SUMMARY

[0003] In view of the above problems existing in the prior art, the present application proposes a kind of left and right circular polarization state fast response light orbital angular momentum high-speed detector and its detection method.

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

[0005] The high-speed optical orbital angular momentum detector with fast response to left and right circular polarization states comprises a high-speed polarization modulation module, an orbital angular momentum photodetector, and an external detection circuit.

[0006] The high-speed polarization modulation module comprises a polarizer with a fixed polarization direction and a photoelastic modulator, the polarizer is arranged in front of the photoelastic modulator to adjust the initial polarization of the light beam carrying orbital angular momentum entering the photoelastic modulator, the photoelastic modulator comprises an optical end and an electrical end, the optical end comprises an optical crystal and piezoelectric transducers arranged on both sides of the optical crystal, the electrical end comprises an electronic driving circuit and a controller, the piezoelectric transducers are connected to the electronic driving circuit, the electronic driving circuit is connected to the controller, the electronic driving circuit applies a sinusoidal varying driving voltage to the piezoelectric transducers of the optical end according to the parameter signal provided by the controller, so as to periodically compress and stretch the optical crystal, 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 transmits through the optical crystal, the optical crystal adds a sinusoidal varying phase difference to the polarization components of the light beam carrying orbital angular momentum along two mutually perpendicular optical axis directions, so as to periodically change the polarization state of the light beam carrying orbital angular momentum, wherein the peak value of the sinusoidal varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator, the polarization direction of the polarizer is adjusted to be 45° with the included angle of the two optical axes of the optical crystal, and the peak value of the phase difference is set to be non-zero, so that the polarization state of the light beam carrying orbital angular momentum transmitting through the optical crystal is periodically changed, and the light beam carrying orbital angular momentum experiences left circular polarization state and right circular polarization state once in a working cycle of the photoelastic modulator through the modulation of the photoelastic modulator.

[0007] The track angular momentum detector comprises a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate is not conductive, and the detection material is arranged on the upper surface of the substrate; the electrode structure is arranged on the detection material and comprises a first detection electrode, a second detection electrode and a contact electrode; wherein the shapes of the first and second detection electrodes are two concentric partial circular rings with different radii respectively, 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 connected to the contact electrode respectively and connected to an external detection circuit through the contact electrode; the light beam carrying the track angular momentum is modulated by a photoelastic modulator, vertically incident to the detection material and located between the first and second detection electrodes, and a net current in 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 excited by left and right circular polarization states of the polarization state of the light beam carrying the track angular momentum have a difference, and the difference of the radial photocurrent responses under excitation of left and right circular polarization light is a circular polarization dependent component of the radial photocurrent response, wherein when the quantum number of the optical track angular momentum changes, the size of the circular polarization dependent component of the radial photocurrent response also changes, and when the quantum number of the optical track angular momentum reverses the sign, the direction of the circular polarization dependent component of the radial photocurrent response also reverses; the light beam carrying the track angular momentum experiences once left circular polarization state and once 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; the first and second detection electrodes collect the radial photocurrent response and output to the external detection circuit.

[0008] The external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photocurrent response by a lock-in amplification technology, and obtains the circular polarization dependent component of the radial photocurrent response; the information of the optical track angular momentum is directly obtained from the circular polarization dependent component of the radial photocurrent response, so that the information of the optical track angular momentum with wide spectral range and fast response is detected at ambient temperature.

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

[0010] The light beam carrying the track angular momentum and having a circular polarization state is in the shape of a circular 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 the track angular momentum changes in the azimuthal angle direction and has a spiral phase gradient. The circular ring-shaped light beam is located between the first and second detection electrodes, 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 into 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, i.e. 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 spatial imbalance of carriers in the detection material, thereby generating a net in-plane current in the detection material, which has two components perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, i.e. a radial photocurrent component and an angular photocurrent component.

[0012] The detection speed of the orbital angular momentum detector is equivalent to the integration time of the lock-in amplifier, and the theoretical upper limit thereof depends on the working frequency of the photoelastic modulator and the OPGE signal-to-noise ratio of the orbital angular momentum detector. At present, based on a photoelastic modulator and an orbital angular momentum detector with a working frequency of 50 kHz, a detection speed of up to 1 kHz can be achieved, which is 4-5 orders of magnitude higher than that of a conventional OAM detection method. The working frequency of the photoelastic modulator refers to the frequency of the driving voltage, and the frequency of the driving voltage is equal to the resonance frequency of the optical crystal; the resonance frequency of the optical crystal is 20 kHz-100 kHz.

[0013] The upper surface of the substrate is not conductive, and the substrate comprises a substrate and a non-conductive layer, and the non-conductive layer is formed on the upper surface of the lower substrate.

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

[0015] The first detection electrode, the second detection electrode and the contact electrode adopt a single-layer conductive metal layer; or comprise two layers: a transition metal layer and a conductive metal layer, and the conductive metal layer is formed on the surface of the transition metal layer, wherein the transition metal layer functions 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 proportion of the partial circular ring shape of the first and second detection electrodes to the entire circular ring shape is the same, and the center lines coincide, and the proportion is 1 / 4-3 / 4.

[0017] The contact electrodes are arranged at the two ends of the first detection electrode and the second detection electrode, one end of which is used to connect an external detection circuit, and the other end is used to form a two-end symmetrical contact electrode, further limiting the current collection range of the first and second detection electrodes, and avoiding the influence of stray light on measurement.

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

[0019] The external detection circuit comprises a preamplifier, a lock-in amplifier and a computer; the first and second detecting electrodes of the track angular momentum detector are connected to the preamplifier; the preamplifier is connected to the photocurrent signal input end of the lock-in amplifier, and the reference signal input end of the lock-in amplifier is simultaneously connected to the electrical end of the photoelastic modulator; the output end of the lock-in amplifier is connected to the computer; the radial photocurrent response collected by the first and second detecting electrodes is input to the lock-in amplifier after being amplified by the preamplifier, the circular polarization dependent component of the radial photocurrent response is directly extracted according to the modulation frequency provided by the electronic driving circuit of the electrical end of the photoelastic modulator as the reference signal, and is transmitted to the computer, and the computer directly obtains the size and sign of the quantum number of the optical track angular momentum through the size and direction of the circular polarization dependent component of the radial photocurrent response.

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

[0021] The high-speed optical track angular momentum detection method with fast response to left and right circular polarization states comprises the following steps:

[0022] 1) generating periodic left and right circular polarization states:

[0023] a) the electronic driving circuit applies a sinusoidal varying driving voltage to the piezoelectric transducer of the optical end according to the parameter signal provided by the controller, so as to periodically compress and stretch the optical crystal; 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 of the optical crystal is periodically changed;

[0024] b) the optical beam carrying the track angular momentum transmits through the optical crystal, and the optical crystal adds a sinusoidal varying phase difference to the two polarization components of the optical beam carrying the track angular momentum along two mutually perpendicular optical axis directions, so as to periodically change the polarization state of the optical beam carrying the track angular momentum, wherein the peak value of the sinusoidal varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator;

[0025] c) by adjusting the polarization direction of the polarizer to be 45° with the two optical axes of the optical crystal, and setting the peak value of the phase difference to be non-zero, the polarization state of the optical beam carrying the track angular momentum passing through the optical crystal is periodically changed, so that the optical beam carrying the track angular momentum experiences left circular polarization state once and right circular polarization state once in a working period of the photoelastic modulator through the modulation of the photoelastic modulator;

[0026] 2) collecting radial photocurrent response:

[0027] a) the beam carrying orbital angular momentum is modulated by the photoelastic modulator, and is normally incident to the detection material and located between the first and second detection electrodes, and generates a net current in the detection material, the net current has a radial photocurrent component and an angular photocurrent component;

[0028] b) the radial photocurrent response excited by the left circular polarization state and the right circular polarization state of the polarization state of the beam carrying orbital angular momentum has a difference, the difference of the radial photocurrent response excited by the left circular polarization light and the right circular polarization light is a circular polarization dependent component of the radial photocurrent response, wherein when the quantum number of the optical orbital angular momentum changes, the size of the circular polarization dependent component of the radial photocurrent response also changes, and when the quantum number of the optical orbital angular momentum reverses the sign, the direction of the circular polarization dependent component of the radial photocurrent response also reverses;

[0029] c) the beam carrying orbital angular momentum experiences once left circular polarization state and once 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 the radial photocurrent response and output to the external detection circuit;

[0031] 3) obtaining the information of the optical orbital angular momentum:

[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 by the lock-in amplification technology, and obtains the circular polarization dependent component of the radial photocurrent response;

[0033] b) directly obtaining the information of the optical orbital angular momentum from the circular polarization dependent component of the radial photocurrent response, so as to realize the detection of the information of the optical orbital angular momentum with wide spectral range and fast response at ambient temperature.

[0034] In a) of step 1), the frequency of the driving voltage is 10 kHz-10 MHz.

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

[0036] In a) of step 3), the external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photocurrent response by the lock-in amplification technology, and obtains the circular polarization dependent component of the radial photocurrent response: the sine signal output by the lock-in amplifier has a coefficient difference with the circular polarization dependent component of the radial photocurrent response, and the amplitude of the sine signal output by the lock-in amplifier is multiplied by a coefficient, so that the circular polarization dependent component of the radial photocurrent response is obtained.

[0037] In b) of step 3), the size and sign of the quantum number of the optical orbital angular momentum are obtained through the size and direction of the circular polarization dependent component of the radial photocurrent response.

[0038] Advantages of the present application:

[0039] The present application is based on high-speed polarization modulation technology and an orbital angular momentum detector, and realizes high-speed detection of information of optical orbital angular momentum; compared with the detection speed of minute order based on the traditional detection method, the detection speed of optical orbital angular momentum is improved to millisecond order, and the quantum number of optical orbital angular momentum can be directly distinguished through the circular polarization dependent component of the radial photocurrent response extracted by the lock-in amplifier, without additional calculation and data processing by a computer; since the photoelastic modulator has a large working wavelength range, the present application can also be applied to detection of optical orbital angular momentum in a large wavelength range; the present application is applied to various application occasions of OAM detection, such as infrared imaging, military investigation and focal plane imaging. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 FIG. 1 is a schematic diagram of an embodiment of the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the present application;

[0041] Figure 2 FIG. 2 is a schematic diagram of the polarization state of the light beam carrying orbital angular momentum changing in one working cycle of the photoelastic modulator in the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the present application;

[0042] Figure 3 FIG. 3 is a schematic diagram of an embodiment of the orbital angular momentum photodetector of the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the present application;

[0043] Figure 4 FIG. 4 is a schematic diagram of the test results of the circular polarization dependent component of the radial photocurrent of an embodiment of the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the present application under the incidence of different light beams carrying orbital angular momentum;

[0044] Figure 5The schematic 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 optical orbital angular momentum under the incidence of different beams carrying the optical orbital angular momentum for an embodiment of the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the application

[0045] Figure 6 The signal-to-noise ratio test results of the circular polarization dependent component of the photocurrent response under different phase-locked amplifier integration time settings for an embodiment of the left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the application. DETAILED DESCRIPTION

[0046] The application will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] As shown in the drawings, Figure 1 The left and right circular polarization state fast response optical orbital angular momentum high-speed detector of the embodiment includes a high-speed polarization modulation module, an orbital angular momentum photodetector 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 in front of the photoelastic modulator to adjust the initial polarization of the beam carrying the 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, the optical axis is perpendicular to the xy plane, the electrical end includes an electronic driving circuit and a controller, the piezoelectric transducers are connected to the electronic driving circuit, the electronic driving circuit is connected to the controller, the electronic driving circuit applies a sinusoidal varying driving voltage to the piezoelectric transducers of the optical end according to the parameter signal provided by the controller, thereby periodically compressing and stretching the optical crystal, a part of the optical crystal is a light transmission part, piezoelectric transducers are respectively arranged on both sides of the other part of the optical crystal, the parameter signal provided by the controller includes the frequency and the peak value of the phase difference of the driving voltage; 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 properties of the optical crystal are periodically changed; the beam carrying the orbital angular momentum passes through the optical crystal, and the optical crystal adds a sinusoidal phase difference to the two mutually perpendicular polarization components of the beam carrying the orbital angular momentum along the optical axis direction, thereby periodically changing the polarization state of the beam carrying the orbital angular momentum, wherein the peak value of the sinusoidal phase difference added by the optical crystal is provided by the parameter setting of the controller of the photoelastic modulator; by adjusting the polarization direction of the polarizer to be 45° with the two optical axes of the optical crystal, and setting the peak value of the phase difference to π / 2, the polarization state of the beam carrying the orbital angular momentum passing through the optical crystal is periodically changed, so that the beam carrying the orbital angular momentum experiences left circular polarization state once and right circular polarization state once in a working cycle of the photoelastic modulator through the modulation of the photoelastic modulator; Figure 1 In the formula, E represents an electric field, and the direction represents the polarization direction of the beam;

[0049] As Figure 3As shown, the track angular momentum detector comprises a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate 1 is not conductive, and the detection material 2 is arranged on the upper surface of the substrate; the electrode structure is arranged on the detection material, and the electrode structure comprises a first detection electrode, a second detection electrode and a contact electrode; wherein the shapes of the first and second detection electrodes are two concentric partial circular rings with the same proportion and the same center line, and the radii of the two concentric partial circular rings are different; the first and second detection electrodes are each a partial circular ring, and the partial circular ring accounts 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 on the outer side of 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 external detection circuit 6 through the contact electrode; the light beam carrying the track angular momentum and having a circular polarization state is in the shape of a circular 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 the track angular momentum changes in the azimuthal direction, and has a spiral phase gradient; the light beam carrying the track angular momentum 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 the track angular momentum is modulated by the photoelastic modulator and is vertically incident on the detection material, the circular ring-shaped light beam is located between the first detection electrode and the second detection electrode, and an electric field parallel to the plane of the detection material and a magnetic field perpendicular to the plane of the detection material, i.e. an in-plane electric field and an out-of-plane magnetic field, are generated; the optical phase of the light beam carrying the track angular momentum vertically incident on the detection material changes in the azimuthal direction, and the spatial gradient of the in-plane electric field and the out-of-plane magnetic field together causes spatial imbalance of carriers in the multilayer graphene; based on the two-dimensional linear energy band structure of the multilayer graphene, the characteristics of high Fermi velocity and long carrier relaxation time, and the significant intraband motion and interband transition of carriers, a strong in-plane net current is generated in the multilayer graphene, and the in-plane net current has two directions of response, i.e. a radial photocurrent response and an angular photocurrent response, which are perpendicular to the spiral phase gradient and parallel to the spiral phase gradient; the radial photocurrent responses excited by left circular polarization and right circular polarization of the polarization state of the light beam carrying the track angular momentum have a difference, and the difference of the radial photocurrent responses under excitation of left circular polarization light and right circular polarization light is a circular polarization dependent component of the radial photocurrent response, wherein when the quantum number of the optical track angular momentum changes, the size of the circular polarization dependent component of the radial photocurrent response also changes, and when the quantum number of the optical track angular momentum reverses the sign, the direction of the circular polarization dependent component of the radial photocurrent response also reverses; the light beam carrying the track angular momentum experiences left circular polarization and right circular polarization once in a working period of the photoelastic modulator, so that the circular polarization dependent component of the radial photocurrent response also experiences 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 the external detection circuit;

[0050] The external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photoelectric current response by phase-locked amplification technology, and obtains the circular polarization dependent component of the radial photoelectric current response; the information of the optical orbital angular momentum is directly obtained from the circular polarization dependent component of the radial photoelectric current response, and the size and sign of the quantum number of the optical orbital angular momentum are obtained through the size and direction of the circular polarization dependent component of the radial photoelectric current response, so that the information of the optical orbital angular momentum with wide spectral range and fast response is detected at ambient temperature.

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

[0052] Figure 4 The radial photoelectric current circular polarization dependent component test results of an embodiment based on the detection means under the incidence of different light beams carrying orbital angular momentum are given, in which the orbital angular momentum detector uses multi-layer graphene as the detection material. The quantum numbers of the six kinds of optical orbital angular momentum are +4, +2, +1, -4, -2 and -1. The on-off test is used in the test process, that is, the light is blocked in 0-15 seconds and 35-50 seconds of the test, and the light is turned on in 15-35 seconds of the test. By calculating the response difference between the light blocking and the light turning on, the component from the electrical interference in the response is excluded, and the circular polarization dependent component of the radial photoelectric current response is obtained. The test results show that when the quantum number of the optical orbital angular momentum is positive, the circular polarization dependent component of the radial photoelectric current response obtained by the detection means is positive. Conversely, when the quantum number of the optical orbital angular momentum is negative, the circular polarization dependent component of the radial photoelectric current response obtained by the detection means is negative. Moreover, the greater the quantum number of the optical orbital angular momentum, the greater the circular polarization dependent component obtained. The test results are consistent with the results based on the traditional detection method, which verifies the ability of the detection means to realize the direct detection of the optical orbital angular momentum.

[0053] Figure 5 The test results of the relationship between the radial photocurrent circular polarization dependent component and the quantum number of the optical orbital angular momentum based on an embodiment of the present application under the incidence of different optical beams carrying the optical orbital angular momentum are given. The radial photocurrent circular polarization dependent component is proportional to the quantum number of the optical orbital angular momentum. The greater the quantum number of the optical orbital angular momentum, the greater the circular polarization dependent component; the quantum number of the optical orbital angular momentum is reversed, and the circular polarization dependent component is also reversed. The quantization response of the optical orbital angular momentum further verifies the feasibility of the detection scheme. In addition, the optical orbital angular momentum detection function and the general light intensity detection function can be performed simultaneously.

[0054] Figure 6 The test results of the signal-to-noise ratio of the radial photocurrent circular polarization dependent component under different phase-locked amplifier integration time settings based on an embodiment of the present application are given. The quantum numbers of the orbital angular momentum carried by the two incident beams used in the test process are +4 and -4, respectively, and the six phase-locked amplifier integration times used are 300 ms, 100 ms, 30 ms, 10 ms, 3 ms and 1 ms, and the test process adopts on-off test. The test results show that for the same quantum number of the optical orbital angular momentum and different phase-locked amplifier integration times, the circular polarization dependent component of the radial photocurrent response obtained by the on-off test is unchanged, and the uncertainty range increases with the decrease of the phase-locked amplifier integration time. The optical orbital angular momentum resolution requires that the circular polarization dependent components of the radial photocurrent responses detected under different quantum numbers of the optical orbital angular momentum have distinguishable differences. Therefore, the test results show that under the existing modulation speed and signal-to-noise ratio, the quantum number resolution of ±4 optical orbital angular momentum with a speed of 1 kHz can be realized based on the present application.

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

Claims

1. A high-speed detector for left and right circular polarization state quick response of optical orbital angular momentum, characterized in that, The high-speed optical orbital angular momentum detector comprises a high-speed polarization modulation module, an orbital angular momentum photoelectric detector and an external detection circuit; the high-speed polarization modulation module comprises a polaroid with a fixed polarization direction and a photoelastic modulator; the polaroid is arranged at the front end of the photoelastic modulator and used for adjusting the initial polarization of the light beam carrying the orbital angular momentum entering the photoelastic modulator; the photoelastic modulator comprises an optical end and an electrical end, wherein the optical end comprises an optical crystal and piezoelectric transducers arranged on both sides of the optical crystal, the electrical end comprises an electronic driving circuit and a controller, the piezoelectric transducers are connected to the electronic driving circuit, the electronic driving circuit is connected to the controller, and the electronic driving circuit applies a sinusoidal driving voltage to the piezoelectric transducers of the optical end according to a parameter signal provided by the controller, so that the optical crystal is periodically compressed and stretched; 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 of the optical crystal is periodically changed; the light beam carrying the orbital angular momentum passes through the optical crystal, the optical crystal adds a sinusoidal phase difference to the polarization components of the light beam carrying the orbital angular momentum along two mutually perpendicular optical axis directions, so that the polarization state of the light beam carrying the orbital angular momentum is periodically changed, wherein the peak value of the sinusoidal phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator; the polarization direction of the polaroid is adjusted to be 45° with the included angle of the two optical axes of the optical crystal, and the peak value of the phase difference is set to be non-zero, so that the polarization state of the light beam carrying the orbital angular momentum passing through the optical crystal is periodically changed, and the light beam carrying the orbital angular momentum experiences left circular polarization state and right circular polarization state once in a working cycle of the photoelastic modulator after the modulation of the photoelastic modulator; The track angular momentum photoelectric detector comprises a substrate, a detection material and an electrode structure; wherein the upper surface of the substrate is not conductive, and the detection material is arranged on the upper surface of the substrate; the electrode structure is arranged on the detection material and comprises a first detection electrode, a second detection electrode and a contact electrode; wherein the shapes of the first and second detection electrodes are two concentric partial circular rings with different radii respectively, 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 connected to the contact electrode respectively and connected to an external detection circuit through the contact electrode; the light beam carrying the track angular momentum is modulated by a photoelastic modulator, vertically incident to the detection material and located between the first and second detection electrodes, and a net current in 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 excited by left and right circular polarization states of the polarization state of the light beam carrying the track angular momentum have a difference, and the difference of the radial photocurrent responses under excitation of left and right circular polarization light is a circular polarization dependent component of the radial photocurrent response, wherein when the quantum number of the optical track angular momentum changes, the size of the circular polarization dependent component of the radial photocurrent response also changes, and when the quantum number of the optical track angular momentum reverses the sign, the direction of the circular polarization dependent component of the radial photocurrent response also reverses; the light beam carrying the track angular momentum experiences once left circular polarization state and once 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; the first and second detection electrodes collect the radial photocurrent response and output to the external detection circuit. The external detection circuit extracts the component with the same frequency as the working frequency of the photoelastic modulator in the radial photocurrent response by a lock-in amplification technology, obtains the circular polarization dependent component of the radial photocurrent response, and directly obtains the information of the optical track angular momentum from the circular polarization dependent component of the radial photocurrent response, so as to realize the detection of the optical track angular momentum with wide spectral range and fast response at ambient temperature.

2. The optical orbital angular momentum hyperspeed detector of claim 1, wherein, The optical crystal adopts zinc selenide, fused quartz, calcium fluoride or silicon.

3. The optical orbital angular momentum hyperspeed detector of claim 1, wherein, The light beam carrying the track angular momentum and having the circular polarization state is in the shape of a circular 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 the track angular momentum changes in the azimuthal angle direction and has a spiral phase gradient.

4. The optical orbital angular momentum hyperspeed detector of claim 1, wherein, The detection material of the track angular momentum photoelectric detector adopts a second-type Weyl semimetal or multilayer graphene.

5. The optical orbital angular momentum hyperspeed detector of claim 1, wherein, The partial circular rings of the first and second detection electrodes have the same proportion of the entire circular ring and the same center line, and the proportion is 1 / 4-3 / 4; the width of the first and second detection electrodes is 2-6 μm; and the distance between the first detection electrode and the second detection electrode is 4-12 μm.

6. The optical orbital angular momentum hyperspeed detector of claim 1, wherein, The external detection circuit comprises a preamplifier, a lock-in amplifier and a computer; the first and second detection electrodes of the track angular momentum photodetector are connected to the preamplifier respectively; the preamplifier is connected to the photocurrent signal input end of the lock-in amplifier, and the reference signal input end of the lock-in amplifier is connected to the electrical end of the photoelastic modulator simultaneously; the output end of the lock-in amplifier is connected to the computer; the radial photocurrent response collected by the first and second detection electrodes is input to the lock-in amplifier after being amplified by the preamplifier, the circular polarization dependent component of the radial photocurrent response is directly extracted according to the modulation frequency provided by the electronic driving circuit of the electrical end of the photoelastic modulator as the reference signal, and is transmitted to the computer, and the computer directly obtains the size and sign of the quantum number of the optical track angular momentum through the size and direction of the circular polarization dependent component of the radial photocurrent response.

7. A method for detecting the left and right circular polarization state fast response optical orbital angular momentum high speed detector according to claim 1, characterized in that, The detection method comprises the following steps: 1) generating periodic left and right circular polarization states: a) the electronic driving circuit applies a sinusoidal varying driving voltage to the piezoelectric transducer of the optical end according to the parameter signal provided by the controller, so that the optical crystal is periodically compressed and stretched; 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 of the optical crystal is periodically changed; b) the optical beam carrying the track angular momentum transmits through the optical crystal, the optical crystal adds a sinusoidal varying phase difference to the two polarization components of the optical beam carrying the track angular momentum along two mutually perpendicular optical axis directions, so that the polarization state of the optical beam carrying the track angular momentum is periodically changed, wherein the peak value of the sinusoidal varying phase difference added by the optical crystal is set by the parameters provided by the controller of the photoelastic modulator; c) by adjusting the polarization direction of the polarizer to be 45° with the two optical axes of the optical crystal, and setting the peak value of the phase difference to be non-zero, the polarization state of the optical beam carrying the track angular momentum that transmits through the optical crystal is periodically changed, so that the polarization state of the optical beam carrying the track angular momentum is modulated by the photoelastic modulator, and in one working period of the photoelastic modulator, the optical beam carrying the track angular momentum experiences once left circular polarization state and once right circular polarization state; 2) collecting radial photocurrent response: a) the optical beam carrying the track angular momentum is modulated by the photoelastic modulator, is perpendicularly incident to the detection material and is located between the first and second detection electrodes, and generates a net current in the plane of the detection material, the net current has a radial photocurrent component and an angular photocurrent component; b) the radial photocurrent responses excited by the left and right circular polarization states of the polarization state of the optical beam carrying the track angular momentum have a difference, and the difference of the radial photocurrent responses under the excitation of left and right circular polarization light is the circular polarization dependent component of the radial photocurrent response, wherein when the quantum number of the optical track angular momentum changes, the size of the circular polarization dependent component of the radial photocurrent response also changes, and when the quantum number of the optical track angular momentum reverses the sign, the direction of the circular polarization dependent component of the radial photocurrent response also reverses. c) the beam carrying orbital angular momentum experiences once left circular polarization state and once right circular polarization state in one working period of the photoelastic modulator, so that the circular polarization dependent component of the radial photocurrent response experiences the same periodic variation and has the same frequency as the working frequency of the photoelastic modulator; d) the first and second probe electrodes collect the radial photocurrent response and output to the external detection circuit; 3) obtaining the information of the optical orbital angular momentum: 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 by the lock-in amplification technique, and obtains the circular polarization dependent component of the radial photocurrent response; b) directly obtaining the information of the optical orbital angular momentum from the circular polarization dependent component of the radial photocurrent response, so as to realize the detection of the information of the optical orbital angular momentum with wide spectral range and fast response at ambient temperature.

8. The method of claim 7, wherein the step of detecting is characterized by, In a) of step 1), the frequency of the driving voltage is 10 kHz-10 MHz.

9. The method of claim 7, wherein the step of detecting is characterized by, In a) of step 2), the optical phase of the beam carrying orbital angular momentum vertically incident to the detection material changes in the azimuthal direction, and the spatial gradient of the in-plane electric field and the out-of-plane magnetic field together causes the spatial imbalance of the carriers in the detection material, based on the two-dimensional linear energy band structure of the detection material, and the characteristics of high Fermi velocity and long carrier relaxation time, through the significant intraband motion and interband transition of the carriers, a strong in-plane net current is generated in the detection material, and the in-plane net current has two directions of response, i.e. the radial photocurrent response and the angular photocurrent response, which are perpendicular to the spiral phase gradient and parallel to the spiral phase gradient.

10. The method of claim 7, wherein the step of detecting is characterized by, In b) of step 3), the size and sign of the quantum number of the optical orbital angular momentum are obtained through the size and direction of the circular polarization dependent component of the radial photocurrent response.

Images