Controllable laser pulse generation device based on FPGA

Abstract

The utility model discloses a controllable laser pulse generating device based on an FPGA, and belongs to the field of quantum communication. The device comprises an RF electric signal modulation module, a laser signal modulation module and a signal sampling and measuring module, wherein the RF electric signal modulation module is respectively connected with the laser signal modulation module and the signal sampling and measuring module; and the laser signal modulation module is connected with the signal sampling and measuring module. According to the utility model, an electric modulation signal with controllable amplitude, phase, repetition frequency, pulse width and signal code pattern is generated through the FPGA to drive the light intensity modulator to realize chopping of continuous light, and a specified pulse signal is obtained.

Description

Technical Field

[0001] The utility model belongs to the field of quantum communication, and specifically relates to a controllable laser pulse generating device based on FPGA. Background Art

[0002] In the long history of information technology development, the traditional asymmetric cryptographic system for information encryption has been conquered by quantum factorization algorithms, and can be easily cracked even today when quantum computers are not yet mature. Therefore, in response to the urgent need for confidential communications in all walks of life, quantum key distribution technology (Quantum Key Distribution, QKD) has achieved unprecedented development.

[0003] In a quantum key distribution device, the transmitting end signal generally has a laser generating an optical signal which is modulated by an IM intensity modulator to generate an optical pulse signal with a fixed repetition frequency and width. Generally, there are two ways to generate a pulse laser signal, one is a switch gain mode, and the second is a continuous optical chopping mode. The switch gain mode generates laser pulse signals, which requires expensive microwave devices and complicated analog circuits to debug, increasing the cost and complexity of the solution, and it is difficult to flexibly control the generation of laser pulses, limiting the application of these solutions in quantum secure communications. The comparative document (CN106229807A) discloses a laser pulse generating device with a center frequency stable power amplification. The comparative document uses continuous optical chopping to generate pulsed light, but with the continuous development of information technology, the working bandwidth of digital chips has been increased to more than 10GHz. Therefore, the utility model can directly use a field programmable logic device (FPGA-Field Programmable Gate Array) to control the generation of pulses, and can directly generate high-quality gain-switched laser pulses, realizing the functions of adjustable parameters such as repetition frequency, pulse width, and delay phase. Utility Model Content

[0004] The utility model aims to overcome the shortcomings of the prior art and proposes a controllable laser pulse generating device based on FPGA to achieve the following purposes: an electrical modulation signal with controllable amplitude, phase, repetition frequency, pulse width and signal pattern is generated by FPGA to drive a light intensity modulator to realize chopping of continuous light and obtain a specified pulse signal.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the utility model is: a controllable laser pulse generating device based on FPGA: the device includes an RF electrical signal modulation module, a laser signal modulation module, and a signal sampling and measurement module, wherein: the RF electrical signal modulation module is respectively connected to the laser signal modulation module and the signal sampling and measurement module; the laser signal modulation module is connected to the signal sampling and measurement module.

[0006] Preferably, the RF electrical signal modulation module includes an FPGA high-speed transceiver, a comparator, and an amplifier, wherein: the output end of the FPGA high-speed transceiver is connected to the input end of the comparator, the output end of the comparator is connected to the input end of the amplifier, and the output end of the amplifier is connected to the laser signal modulation module.

[0007] Preferably, the FPGA high-speed transceiver includes a dynamic phase adjustment module, and the phase of the RF electrical modulation signal is set by the dynamic phase adjustment module.

[0008] Preferably, the laser signal modulation module includes a light intensity modulator, a laser source, and a DC voltage source, wherein: the RF electrical modulation signal generated by the RF electrical signal modulation module is sent to the RF end of the light intensity modulator; the IN end of the light intensity modulator is connected to the laser source; the BIAS end of the light intensity modulator is connected to the DC voltage source; and the OUT end of the light intensity modulator is connected to the signal sampling and measurement module.

[0009] Preferably, the signal sampling and measurement module includes a fixed attenuator, a single photon detector, and a time-to-digital converter, wherein: the input end of the fixed attenuator is connected to the laser signal modulation module, the output end of the fixed attenuator is connected to the input end of the single photon detector, and the output end of the single photon detector is connected to the time-to-digital converter; the single photon detector and the time-to-digital converter are respectively connected to the FPGA high-speed transceiver.

[0010] Preferably, the RF electrical signal modulation module is used to generate an RF electrical modulation signal with controllable amplitude, phase, repetition frequency, pulse width and signal code type through FPGA and output it to the laser signal modulation module; the laser signal modulation module is used to chop and adjust the continuous laser signal according to the RF electrical modulation signal to obtain the required pulse signal; the signal sampling and measurement module is used to sample the pulse signal and measure its parameters.

[0011] The technical effects of the utility model are as follows: (1) while ensuring that the phase of laser pulse photons remains unchanged, the utility model can generate an electrically modulated signal with controllable amplitude, phase, repetition frequency, pulse width, and signal code type through FPGA to generate a narrow pulse; (2) through the measurement of the static extinction ratio, the utility model can obtain a pulse signal with a specified static extinction ratio by adjusting the light intensity modulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a structural diagram of a pulse generating device according to an embodiment of the utility model. DETAILED DESCRIPTION

[0013] The following is a further detailed description of the specific implementation of the utility model through the description of the embodiments with reference to the accompanying drawings, with the purpose of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the utility model concept and technical solution of the utility model and to facilitate its implementation. In order to make the technical solution of the utility model clearer, the utility model is explained through the following embodiments:

[0014] A controllable laser pulse generating device based on FPGA, such as Figure 1 As shown, the device includes an RF electrical signal modulation module (RF: radio frequency signal), a laser signal modulation module, and a signal sampling and measurement module, wherein: the RF electrical signal modulation module is used to generate an RF electrical modulation signal with controllable amplitude, phase, repetition frequency, pulse width, and signal code type through FPGA and output it to the laser signal modulation module; the laser signal modulation module is used to chop and adjust the continuous laser signal according to the RF electrical modulation signal to obtain the required pulse signal; the signal sampling and measurement module is used to sample the pulse signal and measure its parameters. Specifically, in this embodiment, the RF electrical signal modulation module is respectively connected to the laser signal modulation module and the signal sampling and measurement module; the laser signal modulation module is connected to the signal sampling and measurement module. The utility model adopts the design concept of the module, simplifies the circuit, and is easy to implement.

[0015] The RF electrical signal modulation module of this embodiment includes an FPGA high-speed transceiver, a comparator, and an amplifier, wherein: the output end of the FPGA high-speed transceiver is connected to the input end of the comparator, the output end of the comparator is connected to the input end of the amplifier, and the output end of the amplifier is connected to the laser signal modulation module. In actual implementation, the selection of the FPGA chip must ensure that it can call the high-speed transceiver. In this embodiment, the FPGA high-speed transceiver is used to generate an RF electrical modulation signal with controllable phase, repetition frequency, pulse width, and signal code type; the comparator is used to reshape the RF electrical modulation signal output by the FPGA high-speed transceiver to improve the signal quality; the amplifier is used to adjust the amplitude of the shaped RF electrical modulation signal. Further, when the FPGA high-speed transceiver is used, its line rate is first set, and then the repetition frequency, pulse width, and signal code type of the RF electrical modulation signal can be set by modifying its transmission source data; in addition, the FPGA high-speed transceiver of this embodiment also includes a dynamic phase adjustment module (the dynamic phase adjustment technology based on FPGA is a prior art and is not repeated in this utility model), and the dynamic phase adjustment function of the dynamic phase adjustment module is used to realize the setting of the phase of the RF electrical modulation signal.

[0016] The laser signal modulation module of this embodiment includes an optical intensity modulator (IM), a laser source, and a DC voltage source, wherein: the RF electrical modulation signal generated by the RF electrical signal modulation module is sent to the RF end of the optical intensity modulator; the IN end of the optical intensity modulator is connected to the laser source; the BIAS end of the optical intensity modulator is connected to the DC voltage source; and the OUT end of the optical intensity modulator is connected to the signal sampling and measurement module. In this embodiment, the laser source is used to generate a continuous laser signal to the optical intensity modulator; the optical intensity modulator is used to chop the continuous laser signal according to the RF electrical modulation signal generated by the RF electrical signal modulation module to obtain a pulse signal; the DC voltage source is used to achieve fine adjustment of the pulse signal width by modulating the bias voltage BIAS of the optical intensity modulator, and the chopped and adjusted narrow pulse is connected to the optical sampling oscilloscope to observe the single pulse width, thereby finally obtaining the required pulse signal. However, the static extinction ratio of the pulse signal obtained at this time may not reach the required target, so it is necessary to further measure the static extinction ratio and adjust it according to the measurement results.

[0017] The maximum dynamic range between the ON-(or Max) state and the OFF-(or Min) state of the IM intensity modulator output light when there is no external RF electrical signal. The maximum output (ON) and minimum output (OFF) optical power of the optical intensity modulator are measured by adjusting the BIAS bias voltage of the optical intensity modulator, and expressed in dB.

[0018] Specifically, the signal sampling and measurement module of this embodiment is used to measure the static extinction ratio of the pulse signal output by the laser signal modulation module, including a fixed attenuator, a single photon detector, and a time-to-digital converter (TDC-Time-to-Digital Converter), wherein: the input end of the fixed attenuator is connected to the laser signal modulation module, the output end of the fixed attenuator is connected to the input end of the single photon detector, and the output end of the single photon detector is connected to the time-to-digital converter; the single photon detector and the time-to-digital converter are respectively connected to the FPGA high-speed transceiver. In this embodiment, by adjusting the ATT value of the fixed attenuator on the optical path, the BIAS bias voltage of the light intensity modulator, and the phase difference between the RF electrical modulation signal and the single photon detector reference clock, the maximum count and the minimum count are measured to calculate the static extinction ratio. Specifically, the steps for measuring the static extinction ratio are as follows:

[0019] S1. Set the FPGA high-speed transceiver to output an RF electrical modulation signal with a specified repetition frequency and pulse width;

[0020] S2, adjusting the ATT value of the fixed attenuator to attenuate the pulse signal output by the laser signal modulation module to a single photon level;

[0021] S3, adjusting the phase difference between the single photon detector and the RF electrical modulation signal output by the FPGA high-speed transceiver to maximize the count of the single photon detector;

[0022] S4, adjusting the phase difference between the single photon detector and the RF electrical modulation signal output by the FPGA high-speed transceiver, and adjusting the BIAS bias voltage amplitude of the light intensity modulator, using a time-to-digital converter to observe the count of the single photon detector, so that the detector count is minimized, which is recorded as Cmin;

[0023] S5, stop inputting the RF electrical modulation signal output by the laser signal modulation module into the light intensity modulator, and use the time-to-digital converter to observe the count of the single-photon detector, so that the detector count is maximized, which is recorded as Cmax;

[0024] S6, turn off the laser, observe the count of the single photon detector by the time-to-digital converter, and test the dark count of the detector, which is recorded as Cdark;

[0025] S7. Calculate the static extinction ratio ER, where: ER = 10*log[(Cmax-Cdark) / (Cmin-Cdark).

[0026] According to the above device, after the device is powered on, the working principle of the utility model is as follows: first, the phase, repetition frequency, signal code type, and pulse width of the output signal are set through the FPGA high-speed transceiver; then the output signal is shaped through the comparator; finally, the amplitude of the output signal is set through the amplifier; the output signal is judged by the oscilloscope whether it meets the requirements, and when it does not meet the requirements, the amplifier is adjusted to adjust the amplitude of the output signal until the output signal meets the requirements; when the output signal meets the requirements, the output signal is sent to the light intensity modulator for modulation, at this time, the laser source outputs a continuous laser signal to the light intensity modulator, and the DC voltage source outputs a DC voltage to the light intensity modulator to modulate its bias voltage BIAS, and finally a pulse signal is obtained through the output of the light intensity modulator; the pulse signal is sent to the signal sampling and detection module for measurement, and according to the measurement result, the pulse signal is judged by the oscilloscope whether it meets the requirements, and when it does not meet the requirements, the DC voltage source adjusts the pulse signal by modulating the bias voltage BIAS of the light intensity modulator until the pulse signal meets the requirements; when the requirements are met, the final pulse signal is output.

[0027] The utility model generates an electrical modulation signal with controllable amplitude, phase, repetition frequency, pulse width and signal pattern through FPGA to drive IM to generate narrow pulses, and can realize the functions of adjustable parameters such as repetition frequency, pulse width, delay phase, etc.

[0028] The above is an exemplary description of the utility model in conjunction with the accompanying drawings. Obviously, the specific implementation of the utility model is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the utility model; or the above concept and technical solution of the utility model are directly applied to other occasions without improvement, they are all within the protection scope of the utility model.

Claims

1. A controllable laser pulse generating device based on FPGA, characterized in that: The device includes an RF electrical signal modulation module, a laser signal modulation module, and a signal sampling and measurement module, wherein: the RF electrical signal modulation module is connected to the laser signal modulation module and the signal sampling and measurement module respectively; the laser signal modulation module is connected to the signal sampling and measurement module.

2. The FPGA-based controllable laser pulse generating device according to claim 1, characterized in that: The RF electrical signal modulation module includes an FPGA high-speed transceiver, a comparator, and an amplifier, wherein: the output end of the FPGA high-speed transceiver is connected to the input end of the comparator, the output end of the comparator is connected to the input end of the amplifier, and the output end of the amplifier is connected to the laser signal modulation module.

3. The FPGA-based controllable laser pulse generating device according to claim 2, characterized in that: The FPGA high-speed transceiver includes a dynamic phase adjustment module, through which the phase of the RF electrical modulation signal is set.

4. The FPGA-based controllable laser pulse generating device according to claim 1, characterized in that: The laser signal modulation module includes a light intensity modulator, a laser source, and a DC voltage source, wherein: the RF electrical modulation signal generated by the RF electrical signal modulation module is sent to the RF end of the light intensity modulator; the IN end of the light intensity modulator is connected to the laser source; the BIAS end of the light intensity modulator is connected to the DC voltage source; and the OUT end of the light intensity modulator is connected to the signal sampling and measurement module.

5. The FPGA-based controllable laser pulse generating device according to claim 2, characterized in that: The signal sampling and measurement module includes a fixed attenuator, a single photon detector, and a time-to-digital converter, wherein: the input end of the fixed attenuator is connected to the laser signal modulation module, the output end of the fixed attenuator is connected to the input end of the single photon detector, and the output end of the single photon detector is connected to the time-to-digital converter; the single photon detector and the time-to-digital converter are respectively connected to the FPGA high-speed transceiver.

6. The FPGA-based controllable laser pulse generating device according to claim 1, characterized in that: The RF electrical signal modulation module is used to generate an RF electrical modulation signal with controllable amplitude, phase, repetition frequency, pulse width, and signal code type through FPGA and output it to the laser signal modulation module; the laser signal modulation module is used to chop and adjust the continuous laser signal according to the RF electrical modulation signal to obtain the required pulse signal; the signal sampling and measurement module is used to sample the pulse signal and measure its parameters.

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