A laser transient frequency detection device and method

Abstract

The application belongs to the technical field of laser detection, and discloses a laser instantaneous frequency detection device and method, which comprises: a delay self-coherence module, the delay self-coherence module is connected with a laser to be detected, and is used for performing delay self-coherence processing on an output laser signal of the laser to be detected, so as to obtain a to-be-detected laser signal containing an instantaneous phase change of the output laser signal; and a quadrature detection module, the quadrature detection module is connected with the delay self-coherence module, is used for receiving the to-be-detected laser signal, performing quadrature detection on the to-be-detected laser signal, obtaining an instantaneous phase of the output laser signal, and calculating an instantaneous frequency of the output laser signal according to the instantaneous phase. The application can reduce the complexity and cost of a detection system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser detection, in particular to a laser instantaneous frequency detection device and method. BACKGROUND

[0002] A laser sensor usually converts the measured information into the change of laser instantaneous frequency, so that the information of the measured object can be obtained by detecting the laser instantaneous frequency. Since the laser instantaneous frequency is as high as hundreds of terahertz, and the frequency change represented by the detected sensing information is as low as below megahertz, the orders of magnitude of the two are greatly different. Therefore, in the field of laser sensors, a very stable reference source is often needed to detect the instantaneous change of the laser frequency, and the change of the laser instantaneous frequency is obtained by comparing the relative relationship between the laser instantaneous frequency and the reference source. Such a reference source is generally realized by a certain type of optical interferometer. At present, the commonly used laser instantaneous frequency detection methods mainly include an external Mach-Zehnder delay interferometer scheme, an external high-Q optical filter scheme, and an external high-stability laser scheme.

[0003] However, the stability of the external reference source directly affects the accuracy of the laser instantaneous frequency demodulation and sensing measurement. In order to compensate for the influence of environmental factors on the stability of the reference source, a relatively complex servo system is often needed to compensate for the drift of the reference baseline caused by environmental factors, resulting in a more complex overall sensing scheme. At the same time, in order to improve the sensitivity of frequency demodulation, an interferometer or a filter with a steep frequency-intensity conversion curve is often used, which not only improves the sensitivity, but also causes the working area to be narrowed and the dead zone to be expanded. The frequency of the measured laser must be within a more narrow frequency range, so that the sensing system can work normally, which puts forward a relatively strict requirement on the laser sensor and seriously limits the application of the sensing system. In addition, the frequency-intensity conversion curves of various types of optical interferometers and optical filters are mostly not linear curves. Therefore, the working point of the sensing system often needs to be biased in the middle of the most linear working area of the reference source to ensure the linearity of the measurement results as much as possible, that is, a relatively complex bias point control system is needed to stabilize the working point of the system in the linear area. In summary, the frequency-intensity conversion in the prior art has the defects of poor stability of the external reference source, dead zone in frequency demodulation, and insufficient linearity of frequency demodulation, resulting in high complexity and cost and low stability of the system. SUMMARY

[0004] The present application provides a laser instantaneous frequency detection device and method, which can overcome the defects of poor stability of the external reference source, dead zone in frequency demodulation, and insufficient linearity of frequency demodulation caused by the frequency-intensity conversion in the prior art, reduce the complexity and cost of the system, and improve the reliability and stability of the system.

[0005] In a first aspect, the embodiments of the present application provide a laser instantaneous frequency detection device, which comprises:

[0006] a delay self-coherence module, which is connected with the laser to be detected, and is configured to perform delay self-coherence processing on the output laser signal of the laser to be detected, so as to obtain a detection laser signal containing instantaneous phase change of the output laser signal;

[0007] a quadrature detection module, which is connected with the delay self-coherence module, and is configured to receive the detection laser signal, perform quadrature detection on the detection laser signal, obtain the instantaneous phase of the output laser signal, and calculate the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0008] In one of the embodiments, the delay self-coherence module comprises a first coupler, an optical frequency shifter, a second coupler and an optical delay device, and the optical frequency shifter is connected with a radio frequency source.

[0009] The first coupler is connected with the laser to be detected, and is configured to divide the output laser signal of the laser to be detected into a first output laser signal and a second output laser signal.

[0010] The optical delay device is configured to perform time delay on the first output laser signal, so as to obtain a first detection laser signal containing instantaneous phase change.

[0011] The optical frequency shifter is configured to perform frequency shift on the second output laser signal according to the frequency of the radio frequency source, so as to obtain a second detection laser signal containing frequency change.

[0012] The second coupler is configured to re-couple the first detection laser signal and the second detection laser signal together, so as to obtain the detection laser signal.

[0013] The quadrature detection module comprises a first photoelectric detector, a radio frequency domain quadrature demodulator, an instantaneous phase calculation unit and an instantaneous frequency calculation unit, and the local oscillator end of the radio frequency domain quadrature demodulator is connected with the radio frequency source.

[0014] The first photoelectric detector is connected with the second coupler, and is configured to receive the detection laser signal, convert the detection laser signal into a detection electric signal, and send the detection electric signal to the signal end of the radio frequency domain quadrature demodulator.

[0015] The radio frequency domain quadrature demodulator is configured to demodulate I and Q signals according to the detection electric signal.

[0016] The instantaneous phase calculation unit is configured to calculate the instantaneous phase of the output laser signal according to the I and Q signals.

[0017] The instantaneous frequency calculation unit is configured to calculate the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0018] In one of the embodiments, the delay self-coherence module further comprises a polarization controller, two ends of the polarization controller are connected to an output end of the optical delay and an input end of the second coupler respectively;

[0019] The quadrature detection module further comprises two radio frequency filters, input ends of the two radio frequency filters are connected to two output ends of the radio frequency domain quadrature demodulator respectively, and output ends of the two radio frequency filters are connected to two input ends of the instantaneous phase calculation unit respectively.

[0020] In one of the embodiments, the delay self-coherence module comprises a third coupler, a 90° optical mixer and an optical delay;

[0021] The third coupler is connected to the laser to be measured, and is used for dividing the output laser signal of the laser to be measured into a first output laser signal and a second output laser signal;

[0022] The optical delay is used for time delaying the first output laser signal to obtain a first laser to be measured containing instantaneous phase change;

[0023] Two input ends of the 90° optical mixer are connected to the third coupler and the optical delay respectively to receive the first laser to be measured and the second output laser signal, and output a laser to be detected according to the first laser to be measured and the second output laser signal, the laser to be detected comprising a first laser signal and a second laser signal;

[0024] The quadrature detection module comprises two second photoelectric detectors, an instantaneous phase calculation unit and an instantaneous frequency calculation unit;

[0025] The two second photoelectric detectors are connected to two output ends of the 90° optical mixer respectively to convert the first laser signal and the second laser signal into an I channel signal and a Q channel signal respectively;

[0026] The instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I channel signal and the Q channel signal;

[0027] The instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0028] In one of the embodiments, the delay self-coherence module further comprises a polarization controller, two ends of the polarization controller are connected to an output end of the optical delay and an input end of the 90° optical mixer respectively;

[0029] The quadrature detection module further comprises two radio frequency filters, input ends of the two radio frequency filters are connected to output ends of the two second photoelectric detectors respectively, and output ends of the two radio frequency filters are connected to two input ends of the instantaneous phase calculation unit respectively.

[0030] In one embodiment, the instantaneous phase calculation unit is configured to calculate the instantaneous phase of the output laser signal according to the I signal and the Q signal by using a phase calculation formula.

[0031] The phase calculation formula is

[0032] wherein, θ is the instantaneous phase, Q is the Q signal, and I is the I signal.

[0033] In one embodiment, the instantaneous frequency calculation unit is configured to calculate the instantaneous frequency of the output laser signal according to the instantaneous phase and a frequency-phase conversion formula.

[0034] The frequency-phase conversion formula is

[0035] wherein, f is the instantaneous frequency, and Δτ is the relative delay time introduced by the optical delay device between the first output laser signal and the second output laser signal.

[0036] The instantaneous frequency calculation unit is further configured to calculate the actual instantaneous frequency of the to-be-tested laser according to the instantaneous frequency of the output laser signal and a preset formula.

[0037] The preset formula is f a =N·SR+,

[0038] wherein, f a is the actual instantaneous frequency, and N is a non-negative integer.

[0039] In a second aspect, the embodiments of the present application provide a laser instantaneous frequency detection method, which comprises:

[0040] delaying and self-coherently processing the output laser signal of the to-be-tested laser to cause the instantaneous phase change of the output laser signal, and obtaining a to-be-detected laser signal containing the instantaneous phase change of the output laser signal;

[0041] performing quadrature detection on the to-be-detected laser signal to obtain the instantaneous phase of the output laser signal, and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0042] In one embodiment, the delaying and self-coherently processing the output laser signal of the to-be-tested laser to obtain the to-be-detected laser signal containing the instantaneous phase change of the output laser signal comprises:

[0043] dividing the output laser signal of the to-be-tested laser into a first output laser signal and a second output laser signal through a first coupler, outputting the first output laser signal to an optical delay device, and outputting the second output laser signal to an optical frequency shifter, wherein the optical frequency shifter is connected with a radio frequency source.

[0044] delaying the first output laser signal by an optical delay device to obtain a first to-be-detected laser signal containing instantaneous phase change; and

[0045] re-coupling the first to-be-detected laser signal and the second to-be-detected laser signal together by a second coupler to obtain a to-be-detected laser signal;

[0046] quadrature detecting the to-be-detected laser signal to obtain an instantaneous phase of the output laser signal, and calculating an instantaneous frequency of the output laser signal according to the instantaneous phase, comprising:

[0047] converting the to-be-detected laser signal into a to-be-detected electrical signal by a first photoelectric detector, and sending the to-be-detected electrical signal to a signal end of a radio frequency domain quadrature demodulator, a local oscillator end of the radio frequency domain quadrature demodulator being connected to a radio frequency source;

[0048] demodulating an I channel signal and a Q channel signal according to the to-be-detected electrical signal by the radio frequency domain quadrature demodulator;

[0049] calculating the instantaneous phase of the output laser signal according to the I channel signal and the Q channel signal;

[0050] calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0051] In one embodiment, the output laser signal of the to-be-detected laser is subjected to delay self-coherence processing to obtain a to-be-detected laser signal containing instantaneous phase change of the output laser signal, comprising:

[0052] dividing the output laser signal of the to-be-detected laser by a third coupler into a first output laser signal and a second output laser signal;

[0053] delaying the first output laser signal by an optical delay device to obtain a first to-be-detected laser signal containing instantaneous phase change;

[0054] inputting the first to-be-detected laser signal and the second output laser signal into two input ends of a 90° optical frequency mixer respectively to make the 90° optical frequency mixer output a to-be-detected laser signal, the to-be-detected laser signal comprising the first laser signal and the second laser signal;

[0055] quadrature detecting the to-be-detected laser signal to obtain an instantaneous phase of the output laser signal, and calculating an instantaneous frequency of the output laser signal according to the instantaneous phase, comprising:

[0056] converting the first laser signal and the second laser signal into an I channel signal and a Q channel signal by two second photoelectric detectors respectively;

[0057] calculating the instantaneous phase of the output laser signal according to the I channel signal and the Q channel signal;

[0058] calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0059] Compared with the prior art, the technical scheme provided by the embodiment of the application has at least the following beneficial effects:

[0060] The laser instantaneous frequency detection device provided by the embodiment of the application can be connected with the to-be-detected laser through a delay self-coherence module, to perform delay self-coherence processing on the output laser signal of the to-be-detected laser, to obtain a to-be-detected laser signal containing the instantaneous phase change of the output laser signal. The delay self-coherence module takes the to-be-detected signal itself as a reference source, without an external reference source, thereby reducing the system complexity and cost. Then, the to-be-detected laser signal is received by a quadrature detection module, the to-be-detected laser signal is quadrature-detected, the instantaneous phase of the output laser signal is obtained, and the instantaneous frequency of the output laser signal is calculated according to the instantaneous phase. The device adopts the frequency-phase conversion method, can utilize the natural linear relationship between the frequency and the phase, solves the fundamental problem of the nonlinearity of the frequency-intensity detection curve in the prior art, thereby eliminates the need to introduce an external reference source, expands the working area, eliminates the dead zone, and thus no longer needs to bias the working point, thereby simplifying the system complexity, reducing the cost, and improving the reliability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 The structure diagram of the laser instantaneous frequency detection device provided by an embodiment of the application is shown.

[0062] Figure 2 The structure diagram of the laser instantaneous frequency detection device provided by another embodiment of the application is shown.

[0063] Figure 3 The structure diagram of the laser instantaneous frequency detection device provided by another embodiment of the application is shown.

[0064] Figure 4 The structure diagram of the laser instantaneous frequency detection device provided by another embodiment of the application is shown.

[0065] Figure 5 The structure diagram of the laser instantaneous frequency detection device provided by another embodiment of the application is shown.

[0066] Figure 6 The flowchart of the laser instantaneous frequency detection method provided by an embodiment of the application is shown. DETAILED DESCRIPTION

[0067] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0068] Please refer to Figure 1 The embodiment of the present application provides a laser instantaneous frequency detection device, which comprises:

[0069] The delay self-coherence module 100 is connected with the to-be-tested laser, and is used for performing delay self-coherence processing on the output laser signal of the to-be-tested laser to obtain a to-be-detected laser signal containing the instantaneous phase change of the output laser signal.

[0070] When the embodiment is used for laser sensing, the to-be-tested laser is a laser sensor carrying sensing information. At this time, the output laser signal of the to-be-tested laser is the measured laser signal, and the frequency of the output laser signal can be regarded as the frequency of the laser sensor. The delay self-coherence module 100 can be an integrated circuit composed of multiple devices commonly used in the prior art, such as couplers, optical delay devices, optical frequency shift devices, optical mixers, etc., which can realize delay self-coherence processing of optical signals.

[0071] Specifically, the delay self-coherence module 100 performs delay self-coherence on the measured laser signal, so that the subsequent to-be-detected laser signal contains the instantaneous phase change of the measured laser signal. Since the delay self-coherence module 100 is based on the self-coherence principle and uses the measured signal itself as a reference source, it does not need an external reference source, thereby reducing the system complexity and cost.

[0072] The quadrature detection module 200 is connected with the delay self-coherence module 100, and is used for receiving the to-be-detected laser signal, performing quadrature detection on the to-be-detected laser signal, obtaining the instantaneous phase of the output laser signal, and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0073] The quadrature detection module 200 can be an integrated circuit or device composed of multiple modules commonly used in the prior art, such as photodetectors, phase calculation units, frequency calculation units, etc., which can realize the function of optical signal quadrature detection, such as commonly used radio frequency domain quadrature detection circuit and optical domain quadrature detection circuit.

[0074] Specifically, the quadrature detection module 200 can receive the to-be-detected laser signal from the delay self-coherence module 100, and perform quadrature detection on the received to-be-detected laser signal. Since the delay self-coherence module 100 has made the to-be-detected laser signal contain the instantaneous phase change of the measured laser signal by delay self-coherence, the instantaneous phase of the measured laser signal can be obtained, and based on the linear relationship between frequency and phase, the corresponding instantaneous frequency of the measured laser signal, i.e., the instantaneous frequency of the output laser signal, can be obtained from the above instantaneous phase. Therefore, by using the linear relationship between frequency and phase, the instantaneous frequency change of the measured laser signal can be obtained from the instantaneous phase change. Since the linear relationship can accurately measure the frequency change, after using the linear relationship between frequency and phase, the working point at any position does not affect the measurement effect, so there is no need to bias the working point, and therefore there is no need for a complex bias point feedback control system to stabilize the bias point, thereby reducing the complexity and cost of the system and improving the reliability and stability of the system.

[0075] In the above embodiment, the device uses the frequency-phase conversion method, which can utilize the natural linear relationship between frequency and phase to solve the fundamental problem of the nonlinearity of the frequency-intensity detection curve in the prior art, thereby eliminating the need for an external reference source, expanding the working area, eliminating the dead zone, and thus eliminating the need to bias the working point, thereby reducing the complexity and cost of the system and improving the reliability of the system.

[0076] In some embodiments, referring to Figure 2 An embodiment based on a heterodyne structure and radio frequency domain quadrature detection is shown in FIG. 1. The delay self-coherence module 100 includes a first coupler, an optical frequency shifter, a second coupler, and an optical delay device, and the optical frequency shifter is connected with a radio frequency source.

[0077] The first coupler is connected with the to-be-measured laser, and is used to divide the output laser signal of the to-be-measured laser into a first output laser signal and a second output laser signal; the optical delay device is used to time-delay the first output laser signal to obtain a first to-be-detected laser signal containing an instantaneous phase change; the optical frequency shifter is used to frequency-shift the second output laser signal according to the frequency of the radio frequency source to obtain a second to-be-detected laser signal containing a frequency change; and the second coupler is used to recouple the first to-be-detected laser signal and the second to-be-detected laser signal together to obtain the to-be-detected laser signal.

[0078] In the above delay self-coherence module 100, the output laser signal of the laser under test is divided into two output signals by the first coupler: a first output laser signal and a second output laser signal. The second output laser signal is changed in frequency after passing through the optical frequency shifter, and the second output laser signal of the laser under test is obtained. The frequency change is determined by the frequency of the radio frequency source driving the optical frequency shifter. The first output laser signal passes through the optical delay device, thereby introducing a relative time delay with respect to the second output laser signal passing through the optical frequency shifter, and the first output laser signal of the laser under test is obtained. Finally, the above two signals are coupled together by the second coupler, and the laser signal to be detected is output.

[0079] The quadrature detection module 200 includes a first photodetector, a radio frequency domain quadrature demodulator, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit. The local oscillator end of the radio frequency domain quadrature demodulator is connected to the radio frequency source.

[0080] The first photodetector is connected to the second coupler to receive the laser signal to be detected, convert the laser signal to be detected into an electrical signal to be detected, and send the electrical signal to be detected to the signal end of the radio frequency domain quadrature demodulator. The radio frequency domain quadrature demodulator is used to demodulate the I signal and the Q signal according to the electrical signal to be detected. The instantaneous phase calculation unit is used to calculate the instantaneous phase of the output laser signal according to the I signal and the Q signal. The instantaneous frequency calculation unit is used to calculate the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0081] In the above quadrature detection module 200, the laser signal to be detected output by the second coupler is converted into an electrical signal to be detected by the first photodetector, and the electrical signal to be detected is sent to the signal end of the radio frequency domain quadrature demodulator. The local oscillator end of the radio frequency domain quadrature demodulator is connected to the radio frequency source driving the optical frequency shifter, so that the radio frequency domain quadrature demodulator outputs two signals after demodulating the electrical signal to be detected, which are the I signal and the Q signal. The I signal and the Q signal are input into the instantaneous phase calculation unit, and the instantaneous phase of the laser under test is obtained after calculation. The calculated instantaneous phase is converted into the instantaneous frequency of the laser under test in the instantaneous frequency calculation unit.

[0082] In actual implementation, the I and Q signals output by the radio frequency domain quadrature demodulator can be sampled and quantized by an analog-to-digital converter, and then sent to the instantaneous phase calculation unit and the instantaneous frequency calculation unit to obtain the instantaneous frequency of the measured laser. The phase calculation unit and the frequency calculation unit can be implemented by using a commonly used calculation unit in the prior art, such as a single-chip microcomputer, a digital signal processor (DSP), a field programmable gate array (FPGA), a computer, or the like.

[0083] In the above embodiment, the device can use the delay self-coherence module 100 including the coupler, the optical frequency shifter, and the optical delay device, and the heterodyne radio frequency domain quadrature detection to realize the laser instantaneous frequency measurement. The natural linear relationship between the frequency and the phase is used, without introducing an external reference source, eliminating the dead zone, and without biasing the operating point.

[0084] In actual application scenarios, optical amplifiers, electrical amplifiers, filters, polarization controllers, analog-to-digital converters, and other optical or electrical signal control devices can be added at appropriate places according to actual needs to improve the signal-to-noise ratio and other indicators and obtain higher performance.

[0085] Based on the above embodiment, in some embodiments, as shown in Figure 3 The polarization controller can be connected to the output end of the optical delay device and the input end of the second coupler.

[0086] Specifically, the polarization controller is arranged on the branch of the first measured laser signal output by the optical delay device. When the second coupler re-couples the first measured laser signal and the second measured laser signal together, the polarization state of the polarization controller is adjusted to optimally match the polarization states of the above two signals, and the optical power output by the second coupler reaches a maximum value, which helps to improve the signal-to-noise ratio.

[0087] The quadrature detection module 200 further includes two radio frequency filters. The input ends of the two radio frequency filters are respectively connected to the two output ends of the radio frequency domain quadrature demodulator, and the output ends of the two radio frequency filters are respectively connected to the two input ends of the instantaneous phase calculation unit.

[0088] Specifically, the two output ends of the radio frequency domain quadrature demodulator respectively output I and Q signals. The I and Q signals pass through the same radio frequency bandpass filter, and the interference signals and out-of-band noise existing in the two signals are filtered out, thereby improving the detection accuracy.

[0089] In the above embodiment, the device can improve the signal-to-noise ratio by adding a polarization controller, and improve the detection accuracy by setting a radio frequency filter to filter the I and Q signals.

[0090] In some other embodiments, referring to Figure 4 As shown in an embodiment based on a homodyne structure and optical domain quadrature detection, the delay self-coherence module 100 includes a third coupler, a 90° optical mixer, and an optical delay device.

[0091] The third coupler is connected to the laser to be detected, and is used to divide the output laser signal of the laser to be detected into a first output laser signal and a second output laser signal; the optical delay device is used to time-delay the first output laser signal to obtain a first laser to be detected signal containing instantaneous phase change; the two input ends of the 90° optical mixer are connected to the third coupler and the optical delay device respectively to receive the first laser to be detected signal and the second output laser signal, and output a laser to be detected signal according to the first laser to be detected signal and the second output laser signal, the laser to be detected signal including a first laser signal and a second laser signal.

[0092] In the above delay self-coherence module 100, the output laser signal of the laser to be detected is divided by the first coupler into two output signals: the first output laser signal and the second output laser signal. Among them, the second output laser signal is input into the signal end of the 90° optical mixer; the first output laser signal passes through the optical delay device, thereby introducing a relative time delay with respect to the second output laser signal. The optical delay device inputs the obtained first laser to be detected signal into the local oscillator end of the 90° optical mixer. The 90° optical mixer outputs the first laser signal and the second laser signal.

[0093] It should be noted that the above inputting the second output laser signal into the signal end of the 90° optical mixer and inputting the first laser to be detected signal into the local oscillator end of the 90° optical mixer are only for convenience of description, and in actual application, which of the above two branches is connected to the signal end of the 90° optical mixer and which is connected to the local oscillator end of the 90° optical mixer does not matter, and they can be interchanged without affecting.

[0094] The quadrature detection module 200 includes two second photodetectors, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit.

[0095] The two second photodetectors are respectively connected to the two output ends of the 90° optical mixer to convert the first laser signal and the second laser signal into I and Q signals respectively; the instantaneous phase calculation unit is used to calculate the instantaneous phase of the output laser signal according to the I and Q signals; and the instantaneous frequency calculation unit is used to calculate the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0096] The two output signals of the 90° optical mixer are converted into electrical signals by two second photodetectors, which are I and Q signals respectively. The I and Q signals are input into the instantaneous phase calculation unit, and the instantaneous phase of the measured laser is calculated. Then, the calculated instantaneous phase is converted into the instantaneous frequency of the measured laser in the instantaneous frequency calculation unit.

[0097] In the above embodiment, the device can use the delay self-coherent module 100 including the coupler, the 90° optical mixer and the optical delay, and the homodyne optical domain quadrature detection to realize the laser instantaneous frequency measurement. The natural linear relationship between the frequency and the phase is used, without introducing an external reference source, eliminating the dead zone, and without biasing the operating point.

[0098] Based on the above embodiment, in some embodiments, as shown in Figure 5 The delay self-coherent module 100 can further include a polarization controller, and the polarization controller is connected to the output end of the optical delay and the input end of the 90° optical mixer respectively.

[0099] In specific implementation, the polarization state of the polarization controller is adjusted so that the polarization state of the two signals entering the 90° optical mixer is optimally matched, and the optical power output by the 90° optical mixer reaches the maximum value, which helps to improve the signal-to-noise ratio of the embodiment.

[0100] The quadrature detection module 200 can further include two radio frequency filters, and the input ends of the two radio frequency filters are connected to the output ends of the two second photodetectors respectively, and the output ends of the two radio frequency filters are connected to the two input ends of the instantaneous phase calculation unit respectively.

[0101] Among them, the two radio frequency filters can be the same radio frequency low pass filter. Specifically, the two output ends of the radio frequency domain quadrature demodulator output I and Q signals respectively, and the I and Q signals pass through the same radio frequency low pass filter, so as to filter out the interference signals and out-of-band noise existing in the two signals, and improve the detection accuracy.

[0102] In the above embodiment, the device can improve the signal-to-noise ratio by adding a polarization controller, and improve the detection accuracy by setting a radio frequency filter to filter the I and Q signals.

[0103] In some embodiments, the instantaneous phase calculation unit is used to calculate the instantaneous phase of the output laser signal according to the I and Q signals through a phase calculation formula. Specifically, the instantaneous phase calculation unit has two input signals: I and Q signals, which can be denoted as I and Q respectively, and the instantaneous phase θ can be calculated through the phase calculation formula

[0104] ​When the instantaneous phase θ is obtained, and the relative delay time introduced by the optical delay between the first output laser signal and the second output laser signal is known as Δτ, based on the linear relationship between frequency and phase, the instantaneous frequency calculation unit can calculate the instantaneous frequency f according to the frequency-phase conversion formula The instantaneous frequency f of the measured laser is calculated.

[0105] In practical applications, the calculated instantaneous frequency f is not necessarily equal to the actual instantaneous frequency of the measured laser. If the actual instantaneous frequency of the measured laser is denoted as f a , then f a is related to f as follows: f a = N·FSR + f, where FSR (Free Spectral Range) can be referred to as the free spectral width, which is inversely proportional to the relative delay time introduced by the optical delay, that is , where N is a non-negative integer.

[0106] Therefore, the working area of the laser instantaneous frequency detection device in this embodiment is an FSR. Since in sensing applications, only the change of the instantaneous frequency f is concerned, N is not concerned. Therefore, different laser frequencies will automatically obtain different N (and f < FSR) according to the formula f a =N·SR + f, thereby automatically adapting to the long-term stable working frequency of the laser. When the instantaneous frequency of the laser changes by no more than an FSR range, N will not change, and the change of the calculated instantaneous frequency f of the laser reflects the change of the actual instantaneous frequency fa of the laser.

[0107] It should be noted that the specific position of the working area on the frequency spectrum is adaptive, that is, it automatically adapts to the long-term stable working frequency of the laser, and the calculated instantaneous frequency f fluctuates around the long-term stable working frequency, so there is no need to set any bias point. In practical applications, the working area range of the system can be adjusted by adjusting the relative delay time introduced by the optical delay. The device in this embodiment is a linear working area in the entire free spectral width range (FSR), and the frequency domain that can be worked is greatly widened, so that the system has a larger dynamic range.

[0108] Each module in the above laser instantaneous frequency detection device can be realized by software, hardware, and combinations thereof, in whole or in part. The above modules can be embedded in or independent of the processor in the computer device in hardware form, or can be stored in the memory in the computer device in software form, so as to be called and executed by the processor to perform the operations corresponding to the above modules.

[0109] The devices involved in the above embodiments can be replaced by devices with similar functions, such as integrating multiple devices into one device through photoelectric integration and other process means to reduce costs and other purposes. However, these methods do not fundamentally change the principles proposed in the present application and should be considered within the scope of the present application.

[0110] See Figure 6 The embodiment of the present application provides a laser instantaneous frequency detection method, which can include the following steps:

[0111] Step S1, performing delay self-coherence processing on the output laser signal of the to-be-detected laser to obtain a to-be-detected laser signal containing instantaneous phase changes of the output laser signal.

[0112] Specifically, the output laser signal of the to-be-detected laser is subjected to delay self-coherence processing, so that the output laser signal is compared with the phase of itself in the past period of time, and a to-be-detected laser signal containing instantaneous phase changes of the output laser signal is obtained.

[0113] Step S2, performing quadrature detection on the to-be-detected laser signal to obtain the instantaneous phase of the output laser signal, and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.

[0114] In the above embodiment, the method can utilize the natural linear relationship between frequency and phase to solve the fundamental problem of the nonlinearity of the frequency-intensity detection curve in the prior art, thereby eliminating the need to introduce an external reference source, expanding the working area, eliminating the dead zone, and thus no longer needing a bias working point, thereby reducing the complexity and cost of the system and improving the reliability of the system.

[0115] In some embodiments, step S1 can include the following steps:

[0116] The output laser signal of the to-be-detected laser is divided into a first output laser signal and a second output laser signal by a first coupler, the first output laser signal is output to an optical delay device, and the second output laser signal is output to an optical frequency shifter, the optical frequency shifter being connected with a radio frequency source;

[0117] The first output laser signal is subjected to time delay by the optical delay device to obtain a first to-be-detected laser signal containing instantaneous phase changes, and the second output laser signal is subjected to frequency shift by the optical frequency shifter according to the frequency of the radio frequency source to obtain a second to-be-detected laser signal containing frequency changes;

[0118] The first to-be-detected laser signal and the second to-be-detected laser signal are recoupled together by a second coupler to obtain the to-be-detected laser signal;

[0119] Step S2 can include the following steps:

[0120] The first photoelectric detector converts the laser signal to be detected into an electric signal to be detected, and sends the electric signal to be detected to a signal end of the radio frequency domain quadrature demodulator, and a local oscillator end of the radio frequency domain quadrature demodulator is connected to a radio frequency source;

[0121] The radio frequency domain quadrature demodulator demodulates the electric signal to be detected to output an I signal and a Q signal;

[0122] The instantaneous phase of the output laser signal is calculated according to the I signal and the Q signal;

[0123] The instantaneous frequency of the output laser signal is calculated according to the instantaneous phase.

[0124] In some other embodiments, the step S1 can include the following steps:

[0125] The output laser signal of the laser to be detected is divided into a first output laser signal and a second output laser signal by a third coupler;

[0126] The first output laser signal is time-delayed by an optical delay to obtain a first laser signal to be detected containing an instantaneous phase change;

[0127] The first laser signal to be detected and the second output laser signal are respectively input into two input ends of a 90° optical mixer to make the 90° optical mixer output a laser signal to be detected, and the laser signal to be detected includes a first laser signal and a second laser signal;

[0128] The step S2 can include the following steps:

[0129] The first laser signal and the second laser signal are respectively converted into an I signal and a Q signal by two second photoelectric detectors;

[0130] The instantaneous phase of the output laser signal is calculated according to the I signal and the Q signal;

[0131] The instantaneous frequency of the output laser signal is calculated according to the instantaneous phase.

[0132] The specific limitations of the laser instantaneous frequency detection method provided in the above embodiments can refer to the embodiments of the laser instantaneous frequency detection device described above, and will not be repeated here.

[0133] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiments of the methods can be included. Any reference to memory, storage, databases, or other media in the embodiments provided by the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0134] The technical features of the above embodiments can be combined in any way. In order to make the description simple, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0135] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, some modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A laser instantaneous frequency detection device, characterized in that, The device includes: A delayed self-coherent module is connected to the laser under test to perform delayed self-coherent processing on the output laser signal of the laser under test to obtain a laser signal to be detected that includes the instantaneous phase change of the output laser signal. An orthogonal detection module, connected to the delayed autocoherent module, is used to receive the laser signal to be detected, perform orthogonal detection on the laser signal to be detected, obtain the instantaneous phase of the output laser signal, and calculate the instantaneous frequency of the output laser signal based on the instantaneous phase. The delayed autocoherent module includes a first coupler, an optical frequency shifter, a second coupler, and an optical delayer, wherein the optical frequency shifter is connected to an radio frequency source; The first coupler is connected to the laser under test and is used to split the output laser signal of the laser under test into a first output laser signal and a second output laser signal. The optical delay device is used to delay the first output laser signal in time to obtain a first laser signal under test that includes instantaneous phase changes; The optical frequency shifter is used to shift the second output laser signal according to the frequency of the radio frequency source to obtain a second laser signal under test that includes frequency changes. The second coupler is used to recouple the first laser signal to be tested and the second laser signal to be tested together to obtain the laser signal to be detected; The orthogonal detection module includes a first photodetector, a radio frequency domain orthogonal demodulator, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit. The local oscillator terminal of the radio frequency domain orthogonal demodulator is connected to the radio frequency source. The first photodetector is connected to the second coupler to receive the laser signal to be detected, convert the laser signal to be detected into an electrical signal to be detected, and send the electrical signal to be detected to the signal terminal of the radio frequency domain quadrature demodulator. The radio frequency domain quadrature demodulator is used to demodulate and output I-channel and Q-channel signals according to the electrical signal to be detected; The instantaneous phase calculation unit is used to calculate the instantaneous phase of the output laser signal based on the I-channel signal and the Q-channel signal; The instantaneous frequency calculation unit is used to calculate the instantaneous frequency of the output laser signal based on the instantaneous phase.

2. The apparatus according to claim 1, characterized in that, The delayed self-coherent module also includes a polarization controller, the two ends of which are respectively connected to the output of the optical delay unit and the input of the second coupler; The orthogonal detection module further includes two radio frequency (RF) filters. The input terminals of the two RF filters are respectively connected to the two output terminals of the RF domain orthogonal demodulator, and the output terminals of the two RF filters are respectively connected to the two input terminals of the instantaneous phase calculation unit.

3. The apparatus according to claim 1, characterized in that, The delayed autocoherent module includes a third coupler, a 90° optical mixer, and an optical delayer; The third coupler is connected to the laser under test and is used to split the output laser signal of the laser under test into a first output laser signal and a second output laser signal. The optical delay device is used to delay the first output laser signal in time to obtain a first laser signal under test that includes instantaneous phase changes; The two input terminals of the 90° optical mixer are respectively connected to the third coupler and the optical delay unit to receive the first laser signal to be tested and the second output laser signal, and output the laser signal to be detected according to the first laser signal to be tested and the second output laser signal. The laser signal to be detected includes the first laser signal and the second laser signal. The orthogonal detection module includes two second photodetectors, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit; The two second photodetectors are respectively connected to the two output terminals of the 90° optical mixer to convert the first laser signal and the second laser signal into I-channel signals and Q-channel signals, respectively. The instantaneous phase calculation unit is used to calculate the instantaneous phase of the output laser signal based on the I-channel signal and the Q-channel signal; The instantaneous frequency calculation unit is used to calculate the instantaneous frequency of the output laser signal based on the instantaneous phase.

4. The apparatus according to claim 3, characterized in that, The delayed self-coherent module also includes a polarization controller, the two ends of which are respectively connected to the output of the optical delay unit and the input of the 90° optical mixer; The orthogonal detection module also includes two radio frequency (RF) filters. The input terminals of the two RF filters are respectively connected to the output terminals of the two second photodetectors, and the output terminals of the two RF filters are respectively connected to the two input terminals of the instantaneous phase calculation unit.

5. The apparatus according to any one of claims 2 to 4, characterized in that, The instantaneous phase calculation unit is used to obtain the instantaneous phase of the output laser signal based on the I-channel signal and the Q-channel signal using a phase calculation formula; The phase calculation formula is as follows: , in, Let Q be the instantaneous phase, Q be the Q-channel signal, and I be the I-channel signal.

6. The apparatus according to claim 5, characterized in that, The instantaneous frequency calculation unit is used to calculate the instantaneous frequency of the output laser signal according to the instantaneous phase and frequency phase conversion formula; The frequency-phase conversion formula is: , in, The instantaneous frequency, The relative delay time introduced by the optical delay device between the first output laser signal and the second output laser signal; The instantaneous frequency calculation unit is also used to calculate the actual instantaneous frequency of the laser under test based on the instantaneous frequency of the output laser signal and a preset formula; The preset formula is: , in, ; Let N be the actual instantaneous frequency, where N is a non-negative integer.

7. A method for detecting the instantaneous frequency of a laser, characterized in that, The method includes: The output laser signal of the laser under test is split into a first output laser signal and a second output laser signal through a first coupler. The first output laser signal is output to an optical delay unit, and the second output laser signal is output to an optical frequency shifter. The optical frequency shifter is connected to an radio frequency source. The first output laser signal is time-delayed by the optical delayer to obtain a first laser signal under test containing instantaneous phase changes; the second output laser signal is frequency-shifted by the optical frequency shifter according to the frequency of the radio frequency source to obtain a second laser signal under test containing frequency changes. The first laser signal to be tested and the second laser signal to be tested are recoupled together through a second coupler to obtain the laser signal to be detected. The step of performing orthogonal detection on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and calculating the instantaneous frequency of the output laser signal based on the instantaneous phase, includes: The laser signal to be detected is converted into an electrical signal to be detected by a first photodetector, and the electrical signal to be detected is sent to the signal terminal of the radio frequency domain quadrature demodulator. The local oscillator terminal of the radio frequency domain quadrature demodulator is connected to the radio frequency source. The radio frequency domain quadrature demodulator demodulates and outputs I-channel and Q-channel signals based on the electrical signal to be detected. The instantaneous phase of the output laser signal is calculated based on the I-channel signal and the Q-channel signal; The instantaneous frequency of the output laser signal is calculated based on the instantaneous phase. The laser signal to be detected is subjected to orthogonal detection to obtain the instantaneous phase of the output laser signal, and the instantaneous frequency of the output laser signal is calculated based on the instantaneous phase.

8. The method according to claim 7, characterized in that, The output laser signal of the laser under test is subjected to delayed self-coherent processing to obtain a laser signal to be detected that includes the instantaneous phase change of the output laser signal, including: The output laser signal of the laser under test is split into a first output laser signal and a second output laser signal through a third coupler; The first output laser signal is time-delayed by an optical delayer to obtain a first laser signal under test that includes instantaneous phase changes; The first laser signal to be tested and the second output laser signal are respectively input to the two input terminals of a 90° optical mixer so that the 90° optical mixer outputs the laser signal to be tested, the laser signal to be tested including the first laser signal and the second laser signal; The step of performing orthogonal detection on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and calculating the instantaneous frequency of the output laser signal based on the instantaneous phase, includes: The first laser signal and the second laser signal are converted into I-channel signals and Q-channel signals respectively by two second photodetectors; The instantaneous phase of the output laser signal is calculated based on the I-channel signal and the Q-channel signal; The instantaneous frequency of the output laser signal is calculated based on the instantaneous phase.

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