Controllable single-photon system based on pulsed laser and preparation method thereof

Abstract

The application discloses a controllable single-photon system based on pulsed laser and a preparation method thereof, and the system comprises a pulsed laser part and a single-photon generation part, wherein the pulsed laser part comprises a PC terminal upper computer for issuing a command to control a lower computer FPGA to issue a timing trigger TTL pulse signal, an FPGA circuit board for receiving and executing an upper computer control command, a current driver for driving a laser diode to emit light, and a laser diode for emitting pump light; the single-photon generation part comprises a collimation module for filtering collimated pump laser, a single-photon generation module for generating a single-photon signal, and a filtering and collimation module for filtering noise signals and collimating single photons. The application is based on the fact that the number of single photons generated by semiconductor quantum dots excited by adjustable pulsed laser is controllable, so that the preparation of a single-photon source with a controllable number can be realized, and a reference and technical means for absolute calibration of optical devices are provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of controllable single photon source, and particularly relates to a controllable single photon system based on pulsed laser and a preparation method thereof. BACKGROUND

[0002] A single photon source can stably emit a single photon stream, which is a process corresponding to the radiation transition of a single two-level system electron hole pair and embodying the radiation light anti-bunching effect. An ideal single photon source is a regular photon stream with one photon at a certain time interval.

[0003] With the deepening of research on semiconductor quantum dots and the improvement of manufacturing technology and process, the quality of semiconductor quantum dot single photon sources has been greatly improved. However, the current single photon source device does not meet the requirement of emitting only one photon at a time and emitting a certain number of photons as needed at any time. When the laser power is attenuated to the single photon level by using the laser attenuation method for the calibration of optical instruments, the accuracy is limited due to the errors of each link in the system transmission chain. A single photon source that can generate single photons on demand can generate a certain number of single photons in a period of time, so as to design a light source that can accurately calibrate optical instruments. This has very important scientific significance for reducing errors and realizing accurate measurement of data in the field of optical calibration.

[0004] Therefore, it is necessary to design a single photon source system capable of generating controllable single photons. SUMMARY

[0005] In view of the problem of uncontrollable number of single photons generated by the single photon source in the prior art, the present application provides a controllable single photon system based on pulsed laser and a preparation method thereof, so as to generate controllable single photons based on adjustable pulsed laser excitation of semiconductor quantum dots, thereby realizing the preparation of controllable single photon source and providing a reference and technical means for absolute calibration of optical devices.

[0006] In order to achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0007] The controllable single photon system based on pulsed laser comprises a pulsed laser part and a single photon generation part.

[0008] The pulsed laser part comprises a PC terminal host computer, an FPGA circuit board, a current driver and a laser diode.

[0009] The single photon generation part comprises a narrow line filter, a first optical fiber collimator, a wavelength division multiplexer, a low-temperature liquid nitrogen tank, an InAs / GaAs self-organized semiconductor quantum dot sample, a long-pass filter, a narrow-band filter and a second optical fiber collimator.

[0010] The pump light filtering collimation module is formed by the narrow line filter, a first optical fiber collimator; the single photon generation module is formed by the wavelength division multiplexer, a low-temperature liquid nitrogen tank and an InAs / GaAs self-organizing semiconductor quantum dot sample; and the single photon filtering collimation module is formed by the long-pass filter, the narrow band filter and a second optical fiber collimator.

[0011] The PC terminal host computer sends a command to the FPGA circuit board through serial communication, so that the FPGA circuit board generates an electric pulse signal with a frequency of omega1 and a number of n1 and serves as an external trigger source of the current driver;

[0012] The current driver sends a current driving pulse signal with a frequency of omega2 and a number of n2 to the laser diode under the action of the trigger source, so that the laser diode emits pulsed laser with a frequency of omega3 and a number of n3 under the current driving pulse signal, wherein omega1=omega2=omega3 and n1=n2=n3;

[0013] The pump light filtering collimation module filters and collimates the pulsed laser generated by the laser diode, and couples the pulsed laser into a single-mode optical fiber; after focusing through the single-mode optical fiber, the pulsed laser enters the input end of the wavelength division multiplexer in the single photon generation module;

[0014] The wavelength division multiplexer uses the filtered and collimated pulsed laser to excite the InAs / GaAs self-organizing semiconductor quantum dot sample in the low-temperature liquid nitrogen tank and generate a single photon signal output;

[0015] After the single photon signal is filtered by the single photon filtering collimation module to remove non-single photon signals, a pure single quantum fluorescence signal is obtained.

[0016] The controllable single photon system based on pulsed laser also has the characteristics that the radiation lifetime tau of the single quantum fluorescence signal obtained by formula (1) is R :

[0017]

[0018] In formula (1), I0 is the fluorescence intensity of the single photon signal at the initial moment, and I(t) is the fluorescence intensity of the single photon signal at time t.

[0019] When the single pulse width d1 of the pulsed laser generated by the laser diode satisfies formula (2) and the interval d2 between single pulses satisfies formula (3), the InAs / GaAs self-organizing semiconductor quantum dot sample is excited by single pulsed laser and generates a single photon signal:

[0020] d1<delta tau R (2)

[0021] d2>beta tau R(3)

[0022] In formula (2), delta represents the ratio of pulse width to radiation lifetime, and delta is in (0.01, 0.1);

[0023] In formula (3), beta represents the ratio of pulse interval to radiation lifetime, and beta is in (10, 1000).

[0024] The application discloses a controllable single photon preparation method based on pulsed laser.

[0025] The single photon generation part comprises a narrow line filter, a first optical fiber collimator, a wavelength division multiplexer, a low-temperature liquid nitrogen tank, an InAs / GaAs self-organizing semiconductor quantum dot sample, a long-pass filter, a narrow-band filter and a second optical fiber collimator.

[0026] Step 1, the PC end host computer sets the required pulse frequency Data_f and the number Data_n and converts them into the binary numbers Data_f1 and Data_n1 conforming to serial communication;

[0027] Step 2, the PC end host computer writes the converted binary numbers Data_f1 and Data_n1 into the communication unit through a serial port and then transmits them to the serial port receiving communication unit of the FPGA circuit board;

[0028] Step 3, the FPGA circuit board specifies the pulse frequency and number according to the received Data_f2 and Data_n2, thereby generating time sequence electric pulses with a frequency of omega1 and a number of n1 and outputting the electric pulses to the current driver;

[0029] Step 4, the current driver takes the time sequence electric pulses with the frequency of omega1 and the number of n1 as an external trigger source and generates current driving pulse signals with a frequency of omega2 and a number of n2 to the laser diode;

[0030] Step 5, the laser diode emits pulsed laser with a frequency of omega3 and a number of n3 under the driving of the current driving pulse signals with the frequency of omega2 and the number of n2;

[0031] Step 6, the pulsed laser enters the single photon generation part and is filtered and collimated by the narrow line filter and the first optical fiber collimator and then focused into a single-mode optical fiber, the single-mode optical fiber is connected to the input end of the wavelength division multiplexer through a flange adapter, thereby transmitting the filtered and collimated pulsed laser into the wavelength division multiplexer;

[0032] The pulse laser pair of the entering wave division multiplexer pumps and excites the InAs / GaAs self-organizing semiconductor quantum dot sample in a low-temperature liquid nitrogen environment, so that a single quantum fluorescence signal with a number of n is generated;

[0033] Step 7, the single quantum fluorescence signal sequentially passes through background light filtering of a long-pass filter, single-photon spectral filtering of a narrow-band filter and collimation of a second fiber collimator through an outlet end of the wave division multiplexer, so that n pure single quantum fluorescence signals are obtained, wherein n=n3.

[0034] Compared with the prior art, the beneficial effects of the present application are embodied in that:

[0035] 1. The present application adopts a method of exciting self-organizing semiconductor quantum dots to generate single photons with a determined number by using controllable frequency and number of pulse lasers, uses an upper computer to control the FPGA circuit board to send a time sequence pulse as an external trigger source of a current driver, so that the current driver drives a laser diode to generate pulse laser with a pulse width less than at least one order of magnitude of a single photon radiation lifetime and a pulse interval greater than at least one order of magnitude of the single photon radiation lifetime, the pulse frequency and number of the pulse laser are controlled by setting parameters on the upper computer, and then the same number of single photons as the number of pulse laser pulses is obtained, so that the problem of preparing a single photon source for generating single photons with a determined number on demand is overcome, and a technical means is provided for designing an accurate light source for optical instrument calibration.

[0036] 2. The present application adopts a non-resonant excitation method to excite self-organizing semiconductor quantum dots, and compared with the resonant excitation method, the single photon filtering part of the light path is simple and the cost is small. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a whole structure diagram of the preparation system of the present application;

[0038] Figure 2 It is a unit structure diagram for realizing pulse modulation of the present application;

[0039] Figure 3 It is a core diagram of the present application corresponding to a pulse;

[0040] In the figure, 1 is a PC end upper computer, 2 is an FPGA circuit board, 3 is a current driver, 4 is a laser diode, 5 is a narrow-line filter, 6a is a first fiber collimator, 7 is a wave division multiplexer, 8 is a low-temperature liquid nitrogen tank, 9 is an InAs / GaAs self-organizing semiconductor quantum dot sample, 10 is a long-pass filter, 11 is a narrow-band filter, and 6b is a second fiber collimator. DETAILED DESCRIPTION

[0041] In this embodiment, refer to Figure 1A controllable single-photon system based on pulsed laser, comprising: a pulsed laser part, a single-photon generation part;

[0042] The pulsed laser part comprises: a PC host computer 1, an FPGA circuit board 2, a current driver 3, and a laser diode 4.

[0043] The single-photon generation part comprises: a narrow-line filter 5, a first optical fiber collimator 6a, a wavelength division multiplexer 7, a low-temperature liquid nitrogen tank 8, an InAs / GaAs self-organized semiconductor quantum dot sample 9, a long-pass filter 10, a narrow-band filter 11, and a second optical fiber collimator 6b.

[0044] The narrow-line filter 5 and the first optical fiber collimator 6a constitute a pump light filtering and collimating module; the wavelength division multiplexer 7, the low-temperature liquid nitrogen tank 8, and the InAs / GaAs self-organized semiconductor quantum dot sample 9 constitute a single-photon generation module; and the long-pass filter 10, the narrow-band filter 11, and the second optical fiber collimator 6b constitute a single-photon filtering and collimating module.

[0045] The PC host computer 1 sends a command to the FPGA circuit board 2 through serial communication, so that the FPGA circuit board 2 generates an electrical pulse signal with a frequency of ω1 and a number of n1 and serves as an external trigger source of the current driver 3.

[0046] The current driver 3 sends an electrical current pulse signal with a frequency of ω2 and a number of n2 to the laser diode 4 under the action of the trigger source, so that the laser diode 4 emits pulsed laser with a frequency of ω3 and a number of n3 under the electrical current pulse signal, wherein ω1 = ω2 = ω3 and n1 = n2 = n3.

[0047] The pump light filtering and collimating module filters and collimates the pulsed laser generated by the laser diode 4 and couples it into a single-mode optical fiber. After focusing by the single-mode optical fiber, the pulsed laser enters the input end of the wavelength division multiplexer 7 in the single-photon generation module. In the pump light filtering and collimating module, the narrow-line filter 5 filters out optical signals other than the wavelength of the pulsed laser pumped by the laser tube, and the first optical fiber collimator 6a collimates the pulsed laser to convert it into parallel fluorescent light coupled into the single-mode optical fiber.

[0048] The wavelength division multiplexer 7 uses the filtered and collimated pulsed laser to excite the InAs / GaAs self-organized semiconductor quantum dot sample 9 in the low-temperature liquid nitrogen tank 8 and generate single-photon signal output.

[0049] After the single-photon signal is filtered to remove non-single-photon signals by the single-photon filtering and collimating module, a pure single-quantum fluorescent signal is obtained. In the single-photon filtering and collimating module, the long-pass filter 10 filters out the background light present in the single-photon signal, the narrow-band filter 11 filters out the 920 nm single-photon spectral line, and the second optical fiber collimator 6b collimates the single-photon signal into parallel fluorescent light.

[0050] In this embodiment, the fluorescence intensity is proportional to the number of excited-state molecules, and the decay of the single quantum fluorescence signal intensity generated by the quantum dot sample is fitted according to the TCSPC technology using formula (1) to describe the single quantum fluorescence signal intensity generated by the quantum dot sample, and the radiation lifetime τ of the single quantum fluorescence is obtained R :

[0051]

[0052] In formula (1), I0 is the fluorescence intensity of the single photon signal at the initial moment, and I(t) is the fluorescence intensity of the single photon signal at time t.

[0053] In this embodiment, when the single pulse pulse width d1 of the pulsed laser generated by the laser diode (4) satisfies formula (2), and the interval d2 between the single pulses satisfies formula (3), the InAs / GaAs self-organized semiconductor quantum dot sample is excited by the single pulse laser and generates a single photon signal:

[0054] d1<δτ R (2)

[0055] d2>βτ R (3)

[0056] In formula (2), δ represents the ratio of the pulse width to the radiation lifetime, and δ∈(0.01, 0.1);

[0057] In formula (3), β represents the ratio of the pulse interval to the radiation lifetime, and β∈(10, 1000).

[0058] In this embodiment, a controllable single photon preparation method based on pulsed laser is applied to a controllable single photon system composed of a pulsed laser part and a single photon generation part, wherein the pulsed laser part comprises: a PC host computer 1, an FPGA circuit board 2, a current driver 3, and a laser diode 4.

[0059] The single photon generation part comprises: a narrow line filter 5, a first optical fiber collimator 6a, a wavelength division multiplexer 7, a low-temperature liquid nitrogen tank 8, an InAs / GaAs self-organized semiconductor quantum dot sample 9, a long-pass filter 10, a narrow-band filter 11, and a second optical fiber collimator 6b. The controllable single photon preparation method is performed according to the following steps:

[0060] Step 1, the PC host computer 1 sets the required pulse frequency Data_f and the number Data_n and converts them into binary numbers Data_f1 and Data_n1 conforming to serial communication;

[0061] Step 2, PC host 1 converts the received data into the binary number Data_f1 and Data_n1, and writes the converted data into the serial port of the communication unit, and then transmits the data to the serial port receiving communication unit of the FPGA circuit board 2;

[0062] Step 3, the FPGA circuit board 2 determines the pulse frequency and number according to the received Data_f2 and Data_n2, so that the signal generating unit generates a time sequence electric pulse with a frequency of ω1 and a number of n1, and outputs the electric pulse to the current driver 3 through the pulse output unit; wherein, steps 1, 2 and 3 refer to Figure 2 The PC host 1 and the FPGA circuit board 2 correspond to each other to generate a time sequence pulse with a determined frequency and number.

[0063] Step 4, the current driver 3 takes the time sequence electric pulse with a frequency of ω1 and a number of n1 as an external trigger source, and generates a current driving pulse signal with a frequency of ω2 and a number of n2 to the laser diode 4;

[0064] Step 5, the laser diode 4 emits a pulsed laser with a frequency of ω3 and a number of n3 under the driving of the current driving pulse signal with a frequency of ω2 and a number of n2; the pulse width d1 of the pulsed laser satisfies d1 < τ R one order of magnitude, and the interval d2 between the pulses satisfies d2 > τ R at least one order of magnitude, to ensure that there is enough time to generate a single photon when a laser pulse pumps the quantum dot, and the single photon is separated from the single photons generated at other times;

[0065] Step 6, the pulsed laser enters the single photon generation part, and is filtered, collimated and focused into a single-mode fiber through the narrow-line filter 5 and the first fiber collimator 6a in turn, and the single-mode fiber is connected to the input end of the wavelength division multiplexer 7 through a flange adapter, so as to transmit the filtered and collimated pulsed laser to the wavelength division multiplexer 7.

[0066] The pulsed laser entering the wavelength division multiplexer 7 pumps and excites the InAs / GaAs self-organized semiconductor quantum dot sample 9 in the low-temperature liquid nitrogen environment, so as to generate a single quantum fluorescence signal with a number of n; wherein, the public end of the wavelength division multiplexer 7 is connected with the optical fiber coupled to the self-organized semiconductor quantum dot in the single photon source generation device, and the connection between the optical fibers is achieved through the flange adapter.

[0067] Step 7, the single quantum fluorescence signal passes through the background light filtering of the long-pass filter 10, the single photon spectral filtering of the narrow-band filter 11 and the collimation of the second fiber collimator 6b in turn through the outlet end of the wavelength division multiplexer 7, and n pure single quantum fluorescence signals are obtained, wherein n = n3.

[0068] In the embodiment, referring to Figure 3 The core method principle of the number-controllable single-photon system preparation method based on pulsed laser is that when a semiconductor quantum dot is pumped and excited by a light pulse signal with a pulse interval much larger than the radiation lifetime τ R of a single-photon signal and a pulse width much smaller than the radiation lifetime τ R of the single-photon signal, the semiconductor quantum dot generates one single photon under one pulse light excitation. In this way, the number of single photons generated depends on the number of suitable excitation light pulses.

[0069] In summary, the PC terminal host computer 1 controls the FPGA circuit board 2 to generate an external TTL time sequence electrical signal to trigger the current driver 3, and then the laser diode 4 generates a light pulse signal to excite the InAs / GaAs self-organizing semiconductor quantum dot sample 9 to generate a number-controllable single-photon system preparation method meeting the theoretical requirements, so as to meet the requirement of emitting the required number of single photons on demand, and effectively promote the further development of the calibration field of optical instruments.

Claims

1. A controllable single-photon system based on pulsed laser, the features comprising: The pulse laser part, the single photon generation part; The pulse laser part comprises a PC terminal host computer (1), an FPGA circuit board (2), a current driver (3), and a laser diode (4). The single photon generation part comprises a narrow line filter (5), a first optical fiber collimator (6a), a wavelength division multiplexer (7), a low-temperature liquid nitrogen tank (8), an InAs / GaAs self-organizing semiconductor quantum dot sample (9), a long-pass filter (10), a narrow-band filter (11), and a second optical fiber collimator (6b). The narrow line filter (5) and the first optical fiber collimator (6a) constitute a pump light filtering and collimating module; the wavelength division multiplexer (7), the low-temperature liquid nitrogen tank (8), and the InAs / GaAs self-organizing semiconductor quantum dot sample (9) constitute a single photon generation module; and the long-pass filter (10), the narrow-band filter (11), and the second optical fiber collimator (6b) constitute a single photon filtering and collimating module. The PC terminal host computer (1) sends a command to the FPGA circuit board (2) through serial communication, so that the FPGA circuit board (2) generates an electrical pulse signal with a frequency of ω1 and a number of n1 and serves as an external trigger source of the current driver (3). The current driver (3) sends an electrical current driving pulse signal with a frequency of ω2 and a number of n2 to the laser diode (4) under the action of the trigger source, so that the laser diode (4) emits a pulse laser with a frequency of ω3 and a number of n3 under the electrical current driving pulse signal, wherein ω1=ω2=ω3 and n1=n2=n3. The pump light filtering and collimating module filters and collimates the pulse laser generated by the laser diode (4) and couples it into a single-mode optical fiber, and after focusing by the single-mode optical fiber, the pulse laser enters the input end of the wavelength division multiplexer (7) in the single photon generation module. The wavelength division multiplexer (7) uses the filtered and collimated pulse laser to excite the InAs / GaAs self-organizing semiconductor quantum dot sample (9) in the low-temperature liquid nitrogen tank (8) and generates a single photon signal output. After the single photon signal is filtered by the single photon filtering and collimating module to remove non-single photon signals, a pure single quantum fluorescence signal is obtained.

2. A controllable single-photon system based on pulsed laser according to claim 1, characterized in that, The radiative lifetime τ of the single quantum fluorescence signal is obtained using formula (1) R : In formula (1), I0 is the fluorescence intensity of the single photon signal at the initial moment, and I(t) is the fluorescence intensity of the single photon signal at time t.

3. A controllable single-photon system based on pulsed laser according to claim 2, characterized in that, When the single pulse width d1 of the pulse laser generated by the laser diode (4) satisfies formula (2) and the interval d2 between single pulses satisfies formula (3), the InAs / GaAs self-organizing semiconductor quantum dot sample is excited by a single pulse laser and generates a single photon signal: d1 < δτ R (2) d2 > βτ R (3) In formula (2), δ represents the ratio of pulse width to radiative lifetime, and δ∈(0.01, 0.1); In formula (3), β represents the ratio of pulse interval to radiative lifetime, and β∈(10, 1000).

4. A method for controlled single-photon generation based on pulsed laser, characterized in that, The application is applied to a controllable single photon system composed of a pulse laser part and a single photon generation part, wherein the pulse laser part comprises a PC terminal host computer (1), an FPGA circuit board (2), a current driver (3), and a laser diode (4). ​ The single-photon generation part comprises a narrow-line filter (5), a first optical fiber collimator (6a), a wavelength division multiplexer (7), a low-temperature liquid nitrogen tank (8), an InAs / GaAs self-organizing semiconductor quantum dot sample (9), a long-pass filter (10), a narrow-band filter (11), and a second optical fiber collimator (6b). Step 1: The PC host (1) sets the required pulse frequency Data_f and number Data_n and converts them into binary numbers Data_f1 and Data_n1 conforming to serial communication; Step 2: The PC host (1) writes the converted binary numbers Data_f1 and Data_n1 into the serial communication unit and then transmits them to the serial port receiving communication unit of the FPGA circuit board (2); Step 3: The FPGA circuit board (2) specifies the pulse frequency and number according to the received Data_f2 and Data_n2, thereby generating time sequence electric pulses with a frequency of ω1 and a number of n1 and outputting them to the current driver (3); Step 4: The current driver (3) takes the time sequence electric pulses with a frequency of ω1 and a number of n1 as an external trigger source and generates current driving pulse signals with a frequency of ω2 and a number of n2 for the laser diode (4); Step 5: The laser diode (4) emits pulsed laser light with a frequency of ω3 and a number of n3 under the driving of the current driving pulse signals with a frequency of ω2 and a number of n2; Step 6: The pulsed laser light enters the single-photon generation part and is filtered and collimated by the narrow-line filter (5) and the first optical fiber collimator (6a) and then focused into a single-mode optical fiber, which is connected to the input end of the wavelength division multiplexer (7) through a flange adapter, thereby transmitting the filtered and collimated pulsed laser light into the wavelength division multiplexer (7); The pulsed laser light entering the wavelength division multiplexer (7) pumps and excites the InAs / GaAs self-organizing semiconductor quantum dot sample (9) in a low-temperature liquid nitrogen environment, thereby generating single quantum fluorescence signals with a number of n; Step 7: The single quantum fluorescence signals pass through the exit end of the wavelength division multiplexer (7) and then pass through the background light filtering of the long-pass filter (10), the single-photon spectral filtering of the narrow-band filter (11), and the collimation of the second optical fiber collimator (6b), thereby obtaining n pure single quantum fluorescence signals, where n = n3.

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