Direct photoelectric detector of optical orbital angular momentum and detection method thereof

Abstract

The invention discloses a direct photoelectric detector of optical orbital angular momentum and a detection method thereof. According to the invention, a direct photoelectric detector and a focal plane detection array of optical orbital angular momentum are designed based on a first detection electrode and a second detection electrode which are concentric and partially ring-shaped, and multi-layer graphene is adopted as a detection material; as a zero-band-gap material, the multi-layer graphene is wide in detection spectrum range; meanwhile, bias voltage does not need to be applied to detection, and sensitive responsivity is achieved at the room temperature; compared with tantalum-iridium-tellurium, the multilayer graphene has higher photocurrent responsivity and signal-to-noise ratio, so that better optical orbital angular momentum resolution capability is brought; the focal plane detection array of the direct photoelectric detector based on the multi-layer graphene optical orbital angular momentum can realize target tracking and identification, and has a wide application scene in the aspect of military equipment; the invention can be used in the fields of infrared imaging, military reconnaissance, night vision goggles and the like, and can also realize focal plane imaging.

Description

Technical Field

[0001] The invention relates to a light detector, and in particular to a direct photoelectric detector of light orbital angular momentum and a detection method thereof. Background Art

[0002] Recent advances in direct characterization of the topological charge of optical orbital angular momentum (OAM) based on the second-type Weyl semimetals tungsten ditelluride (WTe2) and tantalum iridium telluride (TaIrTe4) have led to the development of direct electrical readout of optical OAM and on-chip integration of focal plane array devices. Based on the orbital photocurrent effect driven by the spiral phase gradient of light, direct optical OAM detection has been achieved in the near-infrared (~1 μm) and mid-infrared (~4 μm) bands. The OAM modes can be distinguished by the quantized values ​​of the current flowing around the beam axis. At present, the materials that have been discovered to have OAM response are limited to the second-type Weyl semimetals. In particular, the only known material for OAM detection in the mid-infrared band is TaIrTe, whose large Berry curvature near the Weyl node enhances the OAM response of TaIrTe in the mid-infrared band. However, both WTe and TaIrTe are unstable under ambient conditions. In particular, for the detection of optical orbital angular momentum in the mid-infrared band, the detection material Tantalum-Iridium-Telluride is a ternary alloy material containing the refractory elements Ta and Ir, which makes large-area epitaxial growth difficult and limits its further use as focal plane arrays and on-chip integration. In addition, the signal-to-noise ratio of the orbital photocurrent response of Tantalum-Iridium-Telluride is still low, which limits its high-speed application in combination with fast circular polarization modulation technology. To promote the large-scale integration of direct photodetection devices of orbital angular momentum, the key is to expand the family of orbital angular momentum sensitive materials and identify candidate materials that are stable under ambient conditions, can be epitaxially grown on a large area on a wafer, and are compatible with the current complementary metal oxide semiconductor (CMOS) technology. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention proposes a direct photoelectric detector of light orbital angular momentum and a detection method thereof.

[0004] An object of the present invention is to provide a direct photodetector of the orbital angular momentum of light.

[0005] The direct photoelectric detector of the optical orbital angular momentum of the present invention comprises: a substrate, multilayer graphene, a first detection electrode, a second detection electrode and a contact electrode; wherein the surface of the substrate is non-conductive; multilayer graphene is formed on the surface of the substrate; the first detection electrode, the second detection electrode and the contact electrode are arranged on the surface of the multilayer graphene, and the first and second detection electrodes are in contact with the multilayer graphene; the first and second detection electrodes are respectively shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide; the first detection electrode is located outside the second detection electrode, and the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode; one end of the first detection electrode and the second detection electrode are respectively connected to an external detection circuit through the contact electrode;

[0006] 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;

[0007] A light beam carrying orbital angular momentum and having a circular polarization state is vertically irradiated onto the multilayer graphene, and the annular light beam is located between a first detection electrode and a 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; the light beam carrying orbital angular momentum is vertically irradiated onto the multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, namely, an in-plane electric field and an out-of-plane magnetic field; the optical phase of the light beam carrying orbital angular momentum changes in the azimuthal direction, and the in-plane electric field and the out-of-plane magnetic field with a spatial gradient jointly cause a spatial imbalance of carriers in the multilayer graphene, based on the multilayer The two-dimensional linear band structure of graphene, as well as the characteristics of high Fermi velocity and long carrier relaxation time, generate a strong in-plane net current in multilayer graphene 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. The difference between the photocurrent response under left-handed circularly polarized light excitation and the photocurrent response under right-handed circularly polarized light excitation is the circularly biased dependent component of the radial photocurrent response. The quantum number and sign of the light orbital angular momentum are related to the size and direction of the circularly biased dependent component of the radial photocurrent response. The light orbital angular momentum The quantum number of the orbital angular momentum of the light is proportional to the circularly polarized component of the radial photocurrent response. When the sign of the quantum number of the orbital angular momentum of the light is reversed, the direction of the circularly polarized component of the radial photocurrent response is also reversed. When the polarization state of the light beam carrying the orbital angular momentum is switched from left-handed circular polarization to right-handed circular polarization, or when the polarization state of the light beam carrying the orbital angular momentum is switched from right-handed circular polarization to left-handed circular polarization, the radial photocurrent response changes. The first detection electrode and the second detection electrode respectively collect the radial photocurrent response perpendicular to the direction of the spiral phase gradient under the excitation of left-handed circular polarized light, and obtain the difference of the photocurrent response under the excitation of left-handed circular polarized light, that is, the circularly polarized value of the radial photocurrent response. The optical path of the photocurrent is detected by a photodetector, and the optical path of the photocurrent is detected by a circularly biased component. The circularly biased component of the radial photocurrent response is used to detect the optical path of the photocurrent. The optical path of the photocurrent is detected by a circularly biased component of the radial photocurrent response ...

[0008] The base comprises a substrate and a non-conductive layer, wherein the non-conductive layer is formed on the upper surface of the substrate of the lower layer.

[0009] The multilayer graphene is formed on the surface of the substrate by arranging prepared multilayer graphene nanosheets on the surface of the substrate, or epitaxially growing multilayer graphene on the substrate, wherein the number of layers of the multilayer graphene is 5 to 50.

[0010] 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.

[0011] The partial ring shapes of the first and second detection electrodes occupy 1 / 4 to 3 / 4 of the entire ring shape.

[0012] 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.

[0013] The width of the first and second detection electrodes is 2-6 micrometers; the distance between the first detection electrode and the second detection electrode is 4-12 micrometers.

[0014] The external detection circuit includes: a preamplifier, a phase-locked amplifier, an optical chopper, a quarter-wave plate and a computer; wherein the first detection electrode and the second detection electrode are respectively connected to the preamplifier through contact electrodes; the preamplifier is connected to the phase-locked amplifier; the phase-locked amplifier is connected to the computer; the optical chopper is placed in the optical path to modulate the light beam at a set modulation frequency, and the reference signal of the modulation frequency is input into the phase-locked amplifier; the quarter-wave plate is placed in the optical path to change the polarization state of the incident light beam by rotation; the radial photocurrent response collected by the first detection electrode and the second detection electrode is amplified by the preamplifier and then input into the phase-locked amplifier, the phase-locked amplifier extracts the corresponding radial photocurrent response according to the modulation frequency provided by the optical chopper, and then separates the net current from the electrical noise, and inputs the obtained net current into the computer; the polarization state of the incident light beam is changed by rotating the quarter-wave plate, and the net current magnitude of the radial photocurrent under the excitation of left-handed circular polarization and right-handed circular polarization is obtained respectively, and then the circularly biased dependent component of the radial photocurrent response is obtained, and the magnitude and sign of the quantum number of the orbital angular momentum are obtained through the circularly biased dependent component of the radial photocurrent response.

[0015] Another object of the present invention is to provide a focal plane detection array of a direct photodetector of light orbital angular momentum.

[0016] The focal plane detection array of the direct photoelectric detector of the optical orbital angular momentum of the present invention comprises: a substrate, multilayer graphene, an electrode structure array and an objective lens; wherein the surface of the substrate is non-conductive; multilayer graphene is formed on the surface of the substrate; the electrode structure array is arranged on the surface of the multilayer graphene; the electrode structure array comprises a plurality of periodically two-dimensionally arranged electrode structure units, each of which comprises a first detection electrode, a second detection electrode and a contact electrode, the first and second detection electrodes are in contact with the multilayer graphene, the first and second detection electrodes are respectively shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide, the first detection electrode is located outside the second detection electrode, the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode, one end of the first detection electrode and the second detection electrode are respectively connected to a channel of an external detection circuit through the contact electrode; the objective lens is arranged above the electrode structure array, and the electrode structure array is located in the focal plane of the objective lens;

[0017] The light beam carrying orbital angular momentum is focused onto the electrode structure array through an objective lens; the light beam carrying orbital angular momentum is in the shape of a circular ring, and the focused circular ring-shaped light spot is located between the first detection electrode and the second detection electrode of an electrode structure unit, and the outer diameter of the light spot is smaller than the inner diameter of the first detection electrode and the inner diameter of the light spot is smaller than the outer diameter of the second detection electrode; the light beam carrying orbital angular momentum is vertically irradiated onto the multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, namely, an in-plane electric field and an out-of-plane magnetic field, generating a strong in-plane net current in the multilayer graphene, and the in-plane net current has two directional responses perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, namely, a radial photocurrent response and angular photocurrent response; the first detection electrode and the second detection electrode respectively collect the radial photocurrent response perpendicular to the spiral phase gradient direction under the excitation of left-handed circularly polarized light, obtain the photocurrent response difference under the excitation of left-handed circularly polarized light, that is, the circular deviation dependence component of the radial photocurrent response, and convert it into an electrical signal and output it to an external detection circuit; the external detection circuit removes the electrical noise in the electrical signal to obtain the radial photocurrent component, directly obtains the information of the orbital angular momentum of the light from the circular deviation dependence component of the radial photocurrent response, obtains the size and sign of the quantum number of the orbital angular momentum through the size and direction of the circular deviation dependence component of the radial photocurrent response, and obtains the required orbital angular momentum image of the incident light through focal plane array detection.

[0018] Another object of the present invention is to provide a detection method of a direct photoelectric detector of light orbital angular momentum.

[0019] The detection method of the direct photoelectric detector of the light orbital angular momentum of the present invention comprises the following steps:

[0020] 1) Direct photodetector setup:

[0021] A multilayer graphene is formed on the surface of a substrate; a first detection electrode, a second detection electrode and a contact electrode are arranged on the surface of the multilayer graphene, and the first and second detection electrodes are in contact with the multilayer graphene; the first and second detection electrodes are shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide; the first detection electrode is located outside the second detection electrode, and the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode; one end of the first detection electrode and the second detection electrode are respectively connected to an external detection circuit through the contact electrode;

[0022] 2) A light beam carrying orbital angular momentum and having a circular polarization state is in a ring shape, 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 light beam carrying orbital angular momentum and having a circular polarization state is vertically irradiated onto the multilayer graphene, and 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;

[0023] 3) The light beam carrying orbital angular momentum is vertically irradiated onto the multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, i.e., an in-plane electric field and an out-of-plane magnetic field; the optical phase of the light beam carrying orbital angular momentum changes in the azimuthal direction, and the in-plane electric field and the out-of-plane magnetic field with spatial gradient jointly cause the spatial imbalance of carriers in the multilayer graphene, and based on the two-dimensional linear energy band structure of the 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 the multilayer graphene through the significant in-band motion and inter-band transition of the carriers, and the in-plane net current has two component responses perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, i.e., a radial photocurrent response and an angular photocurrent response;

[0024] 4) The difference between the photocurrent response under the excitation of left-handed circularly polarized light and the photocurrent response under the excitation of right-handed circularly polarized light is the circularly biased dependent component of the photocurrent response. The quantum number and sign of the orbital angular momentum of light are related to the size and direction of the circularly biased dependent component of the radial photocurrent response. The quantum number of the orbital angular momentum of light is proportional to the circularly biased dependent component of the radial photocurrent response. When the sign of the quantum number of the orbital angular momentum of light is reversed, the direction of the circularly biased dependent component of the radial photocurrent response is also reversed. When the polarization state of the light beam carrying the orbital angular momentum is switched from left-handed circular polarization to right-handed circular polarization, or when the polarization state of the light beam carrying the orbital angular momentum is switched from right-handed circular polarization to left-handed circular polarization, the radial photocurrent response changes.

[0025] 5) The first detection electrode and the second detection electrode collect radial photocurrent responses and convert them into electrical signals and output them to an external detection circuit;

[0026] 6) The external detection circuit removes the electrical noise in the electrical signal to obtain the radial photocurrent component, directly obtains the information of the orbital angular momentum of the light from the circularly biased dependent component of the radial photocurrent, and obtains the size and sign of the quantum number of the orbital angular momentum through the size and direction of the circularly biased dependent component of the radial photocurrent response; multilayer graphene is a zero-bandgap material with a wide detection spectral range, sensitive responsiveness at room temperature, and can work at low temperatures, and does not require and cannot apply an external bias, thereby realizing the detection of information on the orbital angular momentum of light with a wide spectral range and sensitive responsiveness at ambient temperature.

[0027] Advantages of the present invention:

[0028] The present invention is based on concentric partially circular first and second detection electrodes, adopts multilayer graphene as the detection material, and designs a direct photoelectric detector and a focal plane detection array of light orbital angular momentum; multilayer graphene, as a zero-bandgap material, has a wide detection spectrum range; at the same time, detection does not require and cannot require an external bias, and has sensitive response at room temperature; compared with tantalum, iridium and telluride, multilayer graphene has higher photocurrent response and signal-to-noise ratio, which brings better light orbital angular momentum resolution capability; the focal plane detection array of the direct photoelectric detector of the multilayer graphene light orbital angular momentum can realize target tracking and identification, and has broad application scenarios in military equipment; the present invention can be used in the fields of infrared imaging, military reconnaissance and night vision goggles, and can also realize focal plane imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of an embodiment of a direct photodetector of light orbital angular momentum of the present invention;

[0030] Figure 2 A schematic diagram of a direct photoelectric detector of light orbital angular momentum according to an embodiment of the present invention, in which a light beam is vertically irradiated onto a multilayer graphene located between a first detection electrode and a second detection electrode;

[0031] Figure 3 A schematic diagram of the direction of the net current on which the light orbital angular momentum depends, generated after the light beam is vertically irradiated onto the multilayer graphene in one embodiment of the direct photoelectric detector of the light orbital angular momentum of the present invention;

[0032] Figure 4 A schematic diagram of an external detection circuit of an embodiment of a direct photodetector of light orbital angular momentum of the present invention;

[0033] Figure 5 A schematic diagram of a net current generated by an embodiment of a direct photodetector of light orbital angular momentum of the present invention when incident light with different light orbital angular momentum is irradiated;

[0034] Figure 6 A schematic diagram of circular polarization-dependent responses of a net current generated by an embodiment of a direct photodetector of light orbital angular momentum of the present invention when irradiated with incident light of different light orbital angular momentum;

[0035] Figure 7 FIG. 1 is a schematic diagram of an embodiment of a focal plane detection array of a direct photodetector of light orbital angular momentum according to the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0037] like Figure 1 As shown, the direct photoelectric detector of the optical orbital angular momentum of this embodiment includes: a substrate 1, a multilayer graphene 2, a first detection electrode 3, a second detection electrode 4 and a contact electrode 5; wherein the surface of the substrate 1 is non-conductive; the multilayer graphene 2 is formed on the surface of the substrate 1; the first detection electrode 3, the second detection electrode 4 and the contact electrode 5 are arranged on the surface of the multilayer graphene 2, and the first and second detection electrodes 4 are in contact with the multilayer graphene 2; the first and second detection electrodes 4 are respectively shaped as two concentric partial circular rings with different radii, the first detection electrode 3 and the second detection electrode 4 occupy the same proportion of the circular rings, and the center lines coincide; the first detection electrode 3 is located outside the second detection electrode 4, and the inner diameter of the first detection electrode 3 is greater than the outer diameter of the second detection electrode 4; one end of the first detection electrode 3 and the second detection electrode 4 are respectively connected to an external detection circuit 6 through the contact electrode 5;

[0038] like Figure 2 As shown, the light beam 7 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 3 and the inner diameter of the light beam is larger than the outer diameter of the second detection electrode 4; the optical phase of the light beam carrying orbital angular momentum changes in the azimuth direction and has a spiral phase gradient;

[0039] The light beam carrying orbital angular momentum and having circular polarization state is irradiated vertically onto the multilayer graphene 2, and the annular light beam is located between the first detection electrode 3 and the second detection electrode 4. 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 irradiated vertically onto the multilayer graphene 2, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, that is, an in-plane electric field and an out-of-plane magnetic field, such as Figure 3As shown; the optical phase of the light beam carrying orbital angular momentum changes in the azimuthal direction, and the in-plane electric field and out-of-plane magnetic field with spatial gradient jointly cause the spatial imbalance of carriers in the multilayer graphene 2. Based on the two-dimensional linear band structure of the multilayer graphene 2, as well as the characteristics of high Fermi velocity and long carrier relaxation time, a strong in-plane net current is generated in the multilayer graphene 2 through the significant in-band motion and inter-band transition of the carriers. The in-plane net current has two component responses perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, namely the radial photocurrent response and the angular photocurrent response; the difference between the photocurrent response under the excitation of left-handed circularly polarized light and the photocurrent response under the excitation of right-handed circularly polarized light is the circularly biased dependent component of the photocurrent response, and the quantum number and sign of the light orbital angular momentum are related to the size and direction of the circularly biased dependent component of the radial photocurrent response. The quantum of the light's orbital angular momentum is proportional to the circularly polarized component of the radial photocurrent response. When the sign of the quantum number of the light's orbital angular momentum is reversed, the direction of the circularly polarized component of the radial photocurrent response is also reversed. When the polarization state of the light beam carrying the orbital angular momentum is switched from left-handed circular polarization to right-handed circular polarization, or when the polarization state of the light beam carrying the orbital angular momentum is switched from right-handed circular polarization to left-handed circular polarization, the radial photocurrent response changes. The first detection electrode 3 and the second detection electrode 4 collect the radial photocurrent response and convert it into an electrical signal to output to an external detection circuit. The external detection circuit removes the electrical noise in the electrical signal to obtain the radial photocurrent component, directly obtains the information of the light's orbital angular momentum from the circularly polarized component in the radial photocurrent, and obtains the size and sign of the quantum number of the orbital angular momentum through the size and direction of the circularly polarized component of the radial photocurrent response.

[0040] The circular dependence of the radial photocurrent response is proportional to the quantum number of the light's orbital angular momentum, which is given by Figure 5 The experimental results of the given embodiment are verified. Since the positive and negative direction of the circular bias dependence component is related to the setting of the detection circuit, for example, when the phase of the phase-locked amplifier changes by 180 degrees, the circular bias dependence component will also reverse its sign; therefore, it is necessary to first measure the circular bias dependence component of the radial photocurrent response when a light beam carrying a certain OAM is incident, and calibrate the relationship between the positive and negative direction of the circular bias dependence component and the positive and negative orbital angular momentum quantum number. In this embodiment, the OAM quantum number is positive, and the direction of the circular bias dependence component is also positive. After calibration, when a light beam carrying an unknown orbital angular momentum is incident, the size and sign information of the quantum number of the light orbital angular momentum can be directly obtained through the size and direction of the circular bias dependence component of the radial photocurrent response.

[0041] In this embodiment, the substrate 1 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 2 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, the thickness is 10nm, and the upper conductive metal layer is Au, the thickness is 80nm; the thickness of the epitaxially grown multilayer graphene 2 is 25nm; the partial circular rings of the first and second detection electrodes 4 account for 1 / 2 of the entire circular ring; 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, and avoiding stray light from affecting the measurement. The upper conductive metal layer of the transition metal layer is Au, and the thickness is 80nm.

[0042] like Figure 4 As shown, the external detection circuit includes: a preamplifier, a phase-locked amplifier, an optical chopper, a quarter-wave plate and a computer; wherein the first detection electrode 3 and the second detection electrode 4 are respectively connected to the preamplifier through the contact electrode 5; the preamplifier is connected to the phase-locked amplifier; the phase-locked amplifier is connected to the computer; the optical chopper is placed in the optical path to modulate the light beam at a set modulation frequency, and the light signal of the modulation frequency is converted into a reference signal of an electrical signal through the electrical end and input into the phase-locked amplifier; the quarter-wave plate is placed in the optical path after the optical chopper, and changes the polarization state of the incident light beam by rotation; the first detection electrode 3 and the second detection electrode 4 The collected radial photocurrent response is amplified by a preamplifier and then input into a phase-locked amplifier. The phase-locked amplifier extracts the corresponding radial photocurrent response according to the modulation frequency provided by the optical chopper, and then separates the net current from the electrical noise, and inputs the obtained net current into a computer; the polarization state of the incident light beam is changed by rotating a quarter-wave plate, and the net current magnitudes of the radial photocurrent under left-handed circular polarization and right-handed circular polarization excitation are obtained respectively, and then the difference of the photocurrent response under left-handed circular polarization light excitation, i.e., the circularly polarized dependence component of the radial photocurrent response, is obtained, and the magnitude and sign of the quantum number of the orbital angular momentum are obtained through the magnitude of the circularly polarized dependence component of the radial photocurrent response.

[0043] Figure 5The relationship between the photocurrent response and the quarter wave plate angle detected by the photodetector made according to the present invention under the excitation of incident light carrying different orbital angular momentum is given, wherein the polarization state corresponding to the specific quarter wave plate angle is marked in the figure. The quantum numbers of the optical orbital angular momentum (OAM) carried by the six incident lights are +4, +2, +1, -4, -2 and -1 respectively. The photocurrent response changes when the polarization state of the incident light beam is switched from left-handed circular polarization (corresponding to a quarter wave plate angle of 45 degrees) to right-handed circular polarization (corresponding to a quarter wave plate angle of 135 degrees). When the quantum number of the optical orbital angular momentum is positive, the photocurrent under the excitation of left-handed circular polarized light is less than the photocurrent under the excitation of right-handed circular polarized light, and when the quantum number of the optical orbital angular momentum is negative, the photocurrent under the excitation of left-handed circular polarized light is greater than the photocurrent under the excitation of right-handed circular polarized light; at the same time, the size of the corresponding difference of the photocurrent under the excitation of left-handed circular polarized light is related to the size of the quantum number of the optical orbital angular momentum of the excitation light, and the larger the quantum number of the optical orbital angular momentum, the larger the difference. This shows that the direct photodetector of light orbital angular momentum based on multilayer graphene 2 has the ability to realize direct detection of light orbital angular momentum.

[0044] Figure 6 The relationship between the circular polarization-dependent component of the photocurrent response detected by the photodetector prepared according to the present invention under the excitation of incident light carrying different orbital angular momentum and the quantum number of the orbital angular momentum of the incident light is given. The circular polarization-dependent component of the photocurrent is proportional to the quantum number of the orbital angular momentum of the incident light, showing a step-like dependence relationship. The larger the orbital angular momentum of the light, the larger the circular polarization-dependent component of the photocurrent; the sign of the orbital angular momentum of the light is reversed, and the sign of the circular polarization-dependent component of the photocurrent is also reversed. The size and sign of the quantum number of the orbital angular momentum of the light can be directly obtained through the size and sign of the circular polarization-dependent component of the photocurrent response. This result further confirms that the direct photodetector of the orbital angular momentum of light based on multilayer graphene 2 has the ability to realize direct detection of the orbital angular momentum of light.

[0045] Since multilayer graphene is a material without a band gap, photodetectors based on multilayer graphene can be applied to a larger wavelength range and can be used in fields such as infrared imaging, military reconnaissance, and night vision goggles; photodetectors based on multilayer graphene can obtain a higher photocurrent response without providing a bias voltage, and the dark current is very low; in addition, photodetectors based on multilayer graphene can be used at room temperature and do not require a low-temperature environment (such as liquid nitrogen or liquid helium cooling), which is conducive to the miniaturization and economy of the detector. Compared with orbital angular momentum direct detectors based on tantalum, iridium, and tellurium, detectors based on multilayer graphene have higher photocurrent responsivity and signal-to-noise ratio, which brings better optical orbital angular momentum resolution. At the same time, multilayer graphene is a material that is stable under environmental conditions, can be epitaxially grown over a large area, and is compatible with CMOS, which makes detectors based on multilayer graphene more suitable for the integrated application of optical orbital angular momentum direct photodetectors and focal plane detection arrays.

[0046] like Figure 7 As shown, the focal plane detection array of the direct photoelectric detector of the optical orbital angular momentum of this embodiment includes: a substrate 1, a multilayer graphene 2, an electrode structure array 8 and an objective lens 9; wherein the surface of the substrate is non-conductive; the multilayer graphene is epitaxially grown on the surface of the substrate; a part of the area is etched away by oxygen reaction plasma according to a set pattern, and the electrode structure array is set on the surface of the multilayer graphene by photolithography or electron beam exposure; the electrode structure array includes a plurality of periodically two-dimensionally arranged electrode structure units 10, each of which includes a first detection electrode, a second detection electrode and a contact electrode, the first and second detection electrodes are in contact with the multilayer graphene, the first and second detection electrodes are respectively shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide, the first detection electrode is located outside the second detection electrode, the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode, and one end of the first detection electrode and the second detection electrode are respectively connected to a channel of an external detection circuit through the contact electrode; an objective lens is arranged above the electrode structure array, and the electrode structure array is located in the focal plane of the objective lens.

[0047] When a light beam carrying orbital angular momentum is incident, it is first focused to a specific electrode structure unit 5 on the multilayer graphene 2 through an objective lens 9, and a photocurrent is excited in the multilayer graphene; the radial component of the photocurrent is collected by the first detection electrode 3 and the second detection electrode 4 of the electrode structure unit 10 and converted into an electrical signal, which is output to an external detection circuit 6 through the contact electrode 5; the external detection circuit 6 separates the photocurrent part of the electrical signal from the electrical noise, and extracts the circular polarization-dependent component of the photocurrent part, through which the magnitude and sign of the quantum number of the orbital angular momentum carried by the incident light are directly obtained; the orbital angular momentum image of the incident light is directly obtained through the focal plane detection array. In particular, the focal plane detection array of the direct photodetector based on the orbital angular momentum of multilayer graphene light can realize target tracking and identification, and has a wide range of application scenarios in military equipment.

[0048] 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 direct photodetector of light orbital angular momentum, characterized in that: The direct photodetector comprises: a substrate, multilayer graphene, a first detection electrode, a second detection electrode and a contact electrode; wherein the surface of the substrate is non-conductive; multilayer graphene is formed on the surface of the substrate; a first detection electrode, a second detection electrode and a contact electrode are arranged on the surface of the multilayer graphene, and the first and second detection electrodes are in contact with the multilayer graphene; the first and second detection electrodes are shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide; the first detection electrode is located outside the second detection electrode, and the inner diameter of the first detection electrode is larger than the outer diameter of the second detection electrode; one end of the first detection electrode and the second detection electrode are respectively connected to an external detection circuit through the contact electrode; the light beam with orbital angular momentum and 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 orbital angular momentum changes in the azimuth direction and has a spiral phase gradient; A light beam with orbital angular momentum and circular polarization state is vertically irradiated onto multilayer graphene, and the annular light beam is located between a first detection electrode and a 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; the light beam carrying orbital angular momentum is vertically irradiated onto multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, i.e., an in-plane electric field and an out-of-plane magnetic field; the optical phase of the light beam carrying orbital angular momentum changes in the azimuth direction, and the in-plane electric field and the out-of-plane magnetic field with spatial gradient jointly cause spatial imbalance of carriers in the multilayer graphene, based on the multilayer The two-dimensional linear band structure of graphene, as well as the characteristics of high Fermi velocity and long carrier relaxation time, generate a strong in-plane net current in multilayer graphene 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. The difference between the photocurrent response under left-handed circularly polarized light excitation and the photocurrent response under right-handed circularly polarized light excitation is the circularly biased dependent component of the radial photocurrent response. The quantum number and sign of the light orbital angular momentum are related to the size and direction of the circularly biased dependent component of the radial photocurrent response. The light orbital angular momentum The quantum number of the orbital angular momentum of the light is proportional to the circularly polarized component of the radial photocurrent response. When the sign of the quantum number of the orbital angular momentum of the light is reversed, the direction of the circularly polarized component of the radial photocurrent response is also reversed. When the polarization state of the light beam carrying the orbital angular momentum is switched from left-handed circular polarization to right-handed circular polarization, or when the polarization state of the light beam carrying the orbital angular momentum is switched from right-handed circular polarization to left-handed circular polarization, the radial photocurrent response changes. The first detection electrode and the second detection electrode respectively collect the radial photocurrent response perpendicular to the direction of the spiral phase gradient under the excitation of left-handed circular polarized light, and obtain the difference of the photocurrent response under the excitation of left-handed circular polarized light, that is, the circularly polarized value of the radial photocurrent response. The optical path of the photocurrent is detected by a photodetector, and the optical path of the photocurrent is detected by a circularly biased component. The circularly biased component of the radial photocurrent response is used to detect the optical path of the photocurrent. The optical path of the photocurrent is detected by a circularly biased component of the radial photocurrent response ...

2. The direct photodetector according to claim 1, characterized in that The base comprises a substrate and a non-conductive layer, and the non-conductive layer is formed on the upper surface of the substrate of the lower layer.

3. The direct photodetector according to claim 1, characterized in that The multilayer graphene is formed on the surface of the substrate by arranging prepared multilayer graphene nanosheets on the surface of the substrate, or epitaxially growing multilayer graphene on the substrate, wherein the number of layers of the multilayer graphene is 5 to 50.

4. The direct photodetector according to claim 1, characterized in that The first detection electrode, the second detection electrode and the contact electrode are formed of a single conductive metal layer; or include two layers: a transition metal layer and a conductive metal layer, wherein the conductive metal layer is formed on the surface of the transition metal layer, wherein the function of the transition metal layer is to make the conductive metal layer more firmly adhere to the surface of the multilayer graphene.

5. The direct photodetector according to claim 4, characterized in that The conductive metal layer is made of Au, Al or Cu.

6. The direct photodetector according to claim 1, characterized in that The partial ring shapes of the first and second detection electrodes occupy 1 / 4 to 3 / 4 of the entire ring shape.

7. The direct photodetector according to claim 1, characterized in that 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.

8. The direct photodetector according to claim 1, characterized in that The external detection circuit includes: a preamplifier, a phase-locked amplifier, an optical chopper, a quarter-wave plate and a computer; wherein the first detection electrode and the second detection electrode are respectively connected to the preamplifier through contact electrodes; the preamplifier is connected to the phase-locked amplifier; the phase-locked amplifier is connected to the computer; the optical chopper is placed in the optical path to modulate the light beam at a set modulation frequency, and the reference signal of the modulation frequency is input into the phase-locked amplifier; the quarter-wave plate is placed in the optical path to change the polarization state of the incident light beam by rotation; the radial photocurrent response collected by the first detection electrode and the second detection electrode is amplified by the preamplifier and then input into the computer To the phase-locked amplifier, the phase-locked amplifier extracts the corresponding radial photocurrent response according to the modulation frequency provided by the optical chopper, and then separates the net current from the electrical noise, and inputs the obtained net current into a computer; by rotating the quarter-wave plate to change the polarization state of the incident light beam, the net current magnitude of the radial photocurrent under left-handed circular polarization and right-handed circular polarization excitation is obtained respectively, and then the circular polarization dependence component of the radial photocurrent response is obtained, and through the circular polarization dependence component of the radial photocurrent response, the circular polarization dependence component of the radial photocurrent response is obtained, and through the circular polarization dependence component of the radial photocurrent response, the magnitude and sign of the quantum number of the orbital angular momentum are obtained.

9. A focal plane detection array of a direct photodetector of light orbital angular momentum as claimed in claim 1, characterized in that: The focal plane detection array comprises: a substrate, multilayer graphene, an electrode structure array and an objective lens; wherein the surface of the substrate is non-conductive; multilayer graphene is formed on the surface of the substrate; an electrode structure array is arranged on the surface of the multilayer graphene; the electrode structure array comprises a plurality of periodically two-dimensionally arranged electrode structure units, each electrode structure unit comprises a first detection electrode, a second detection electrode and a contact electrode, the first and second detection electrodes are in contact with the multilayer graphene, the first and second detection electrodes are respectively shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide, the first detection electrode is located outside the second detection electrode, the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode, one end of the first detection electrode and the second detection electrode are respectively connected to a channel of an external detection circuit through the contact electrode; an objective lens is arranged above the electrode structure array, and the electrode structure array is located at the focal plane of the objective lens; The light beam carrying orbital angular momentum is focused onto the electrode structure array through an objective lens; the light beam carrying orbital angular momentum is in the shape of a circular ring, and the focused circular ring-shaped light spot is located between the first detection electrode and the second detection electrode of an electrode structure unit, and the outer diameter of the light spot is smaller than the inner diameter of the first detection electrode, and the inner diameter of the light spot is smaller than the outer diameter of the second detection electrode; the light beam carrying orbital angular momentum is vertically irradiated onto the multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, namely, an in-plane electric field and an out-of-plane magnetic field, generating a strong in-plane net current in the multilayer graphene, and the in-plane net current has a magnetic field perpendicular to the spiral phase gradient and parallel to the spiral phase. The invention discloses a method for detecting the spiral phase gradient of a light emitting diode (LED). The method comprises the following steps: firstly detecting the light emitting diode (LED) and the second detecting electrode (detecting the light emitting diode (LED) of the invention respectively, collecting the radial photocurrent response perpendicular to the spiral phase gradient direction under the excitation of left-handed circularly polarized light and right-handed circularly polarized light, obtaining the photocurrent response difference under the excitation of left-handed circularly polarized light, namely the circularly polarized dependence component of the radial photocurrent response, and converting it into an electrical signal and outputting it to an external detection circuit; the external detection circuit removes the electrical noise in the electrical signal to obtain the radial photocurrent component, directly obtains the information of the light orbital angular momentum from the circularly polarized dependence component of the radial photocurrent response, and obtains the required light orbital angular momentum image of the incident light through focal plane array detection.

10. A detection method of a direct photoelectric detector of light orbital angular momentum as claimed in claim 1, characterized in that: The detection method comprises the following steps: 1) Direct photodetector setup: A multilayer graphene is formed on the surface of a substrate; a first detection electrode, a second detection electrode and a contact electrode are arranged on the surface of the multilayer graphene, and the first and second detection electrodes are in contact with the multilayer graphene; the first and second detection electrodes are shaped as two concentric partial circular rings with different radii, the first detection electrode and the second detection electrode occupy the same proportion of the circular rings, and the center lines coincide; the first detection electrode is located outside the second detection electrode, and the inner diameter of the first detection electrode is greater than the outer diameter of the second detection electrode; one end of the first detection electrode and the second detection electrode are respectively connected to an external detection circuit through the contact electrode; 2) A light beam carrying orbital angular momentum and having a circular polarization state, which is in a ring shape, 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 changes in the azimuth direction and has a spiral phase gradient; 3) A light beam carrying orbital angular momentum and having a circular polarization state is vertically irradiated onto the multilayer graphene, and the annular 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; 4) The light beam carrying orbital angular momentum is vertically irradiated onto the multilayer graphene, generating an electric field parallel to the plane of the multilayer graphene and a magnetic field perpendicular to the plane of the multilayer graphene, i.e., an in-plane electric field and an out-of-plane magnetic field; the optical phase of the light beam carrying orbital angular momentum changes in the azimuthal direction, and the in-plane electric field and the out-of-plane magnetic field with spatial gradient jointly cause the spatial imbalance of carriers in the multilayer graphene, and based on the two-dimensional linear energy band structure of the 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 the multilayer graphene through the significant in-band motion and inter-band transition of the carriers, and the in-plane net current has two component responses perpendicular to the spiral phase gradient and parallel to the spiral phase gradient, i.e., a radial photocurrent response and an angular photocurrent response; 5) The difference between the photocurrent response under the excitation of left-handed circularly polarized light and the photocurrent response under the excitation of right-handed circularly polarized light is the circularly biased dependent component of the radial photocurrent response. The quantum number and sign of the orbital angular momentum of light are related to the size and direction of the circularly biased dependent component of the radial photocurrent response. The quantum number of the orbital angular momentum of light is proportional to the circularly biased dependent component of the radial photocurrent response. When the sign of the quantum number of the orbital angular momentum of light is reversed, the direction of the circularly biased dependent component of the radial photocurrent response is also reversed. When the polarization state of the light beam carrying the orbital angular momentum is switched from left-handed circular polarization to right-handed circular polarization, or when the polarization state of the light beam carrying the orbital angular momentum is switched from right-handed circular polarization to left-handed circular polarization, the radial photocurrent response changes. 6) The first detection electrode and the second detection electrode respectively collect radial photocurrent responses perpendicular to the spiral phase gradient direction under the excitation of left-handed circularly polarized light and right-handed circularly polarized light, obtain the photocurrent response difference under the excitation of left-handed circularly polarized light, i.e., the circular polarization-dependent component of the radial photocurrent response, and convert it into an electrical signal and output it to an external detection circuit; 7) The external detection circuit removes the electrical noise in the electrical signal to obtain the radial photocurrent component, directly obtains the information of the orbital angular momentum of the light from the circularly biased component of the radial photocurrent response, and obtains the size and sign of the quantum number of the orbital angular momentum through the size and direction of the circularly biased component of the radial photocurrent response; multilayer graphene is a zero-bandgap material with a wide detection spectral range, sensitive responsiveness at room temperature, and can work at low temperatures, and does not require and cannot apply an external bias, thereby realizing the detection of information on the orbital angular momentum of light with a wide spectral range and sensitive responsiveness at ambient temperature.

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