CN115931145A - Laser instantaneous frequency detection device and method - Google Patents
Laser instantaneous frequency detection device and method Download PDFInfo
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Abstract
The application belongs to the technical field of laser detection and discloses a laser instantaneous frequency detection device and a method, wherein the device comprises: the delay self-coherent module is connected with the laser to be detected and is used for carrying out delay self-coherent processing on the output laser signal of the laser to be detected to obtain the laser signal to be detected containing the instantaneous phase change of the output laser signal; and the orthogonal detection module is connected with the delayed self-coherent module and is used for receiving the laser signal to be detected, carrying out orthogonal detection on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and calculating according to the instantaneous phase to obtain the instantaneous frequency of the output laser signal. The method and the device can achieve the effect of reducing the complexity and the cost of the detection system.
Description
Technical Field
The application relates to the technical field of laser detection, in particular to a laser instantaneous frequency detection device and method.
Background
The laser sensor generally converts the measured information into a change in the instantaneous frequency of the laser light, so that the information of the measured object can be acquired by detecting the instantaneous frequency of the laser light. Because the instantaneous frequency of the laser reaches hundreds of terahertz orders, the frequency change represented by the detected sensing information is as low as below megahertz orders, and the orders of magnitude of the two differ greatly. Therefore, in the field of laser sensors, detecting the instantaneous change of the laser frequency often requires a very stable reference source, 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 reference sources are typically implemented by some type of optical interferometer. At present, the commonly used laser instantaneous frequency detection method mainly comprises an external Mach-Zehnder delay interferometer scheme, an external high Q-value optical filter scheme, an external high stability laser scheme and the like.
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 more complex servo system is often required to be provided to compensate for the drift of the reference baseline caused by correcting the environmental factors, so that the overall sensing scheme is more complex. Meanwhile, in order to improve the sensitivity to frequency demodulation, an interferometer or a filter having a steep frequency-intensity conversion curve is often used, which brings about the problems of reduction of a working area and expansion of a dead zone while improving the sensitivity. The frequency of the laser to be detected must be within a narrower frequency range, and the sensing system can normally work, so that the laser sensor is subjected to more severe requirements, and the application of the sensing system is severely limited. In addition, the frequency-intensity conversion curve of various types of optical interferometers and optical filters is not a linear curve in most cases. Therefore, the operating point of the sensing system can only be biased in the middle of the most linear operating region of the reference source, so as to ensure the linearity of the measurement result as much as possible, i.e. a more complex bias point control system is needed to stabilize the operating point of the system in the linear region. 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, which results in high complexity and cost of the system and low stability.
Disclosure of Invention
The application provides a laser instantaneous frequency detection device and method, which can overcome the defects of poor stability of an external reference source, dead zone of frequency demodulation and insufficient linearity of frequency demodulation caused by frequency-intensity conversion in the prior art, reduce the complexity and cost of a system, and improve the reliability and stability of the system.
In a first aspect, an embodiment of the present application provides a laser instantaneous frequency detection apparatus, including:
the delay self-coherent module is connected with the laser to be detected and is used for carrying out delay self-coherent processing on the output laser signal of the laser to be detected to obtain the laser signal to be detected containing the instantaneous phase change of the output laser signal;
and the orthogonal detection module is connected with the delayed self-coherent module and is used for receiving the laser signal to be detected, carrying out orthogonal detection on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and calculating according to the instantaneous phase to obtain the instantaneous frequency of the output laser signal.
In one embodiment, the delayed self-coherent module comprises a first coupler, an optical frequency shifter, a second coupler and an optical delayer, wherein the optical frequency shifter is connected with a radio frequency source;
the first coupler is connected with the laser to be tested and used for dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal;
the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change;
the optical frequency shifter is used for shifting the frequency of the second output laser signal according to the frequency of the radio frequency source to obtain a second laser signal to be detected containing frequency change;
the second coupler is used for re-coupling the first laser signal to be detected and the second laser signal to be detected together to obtain a laser signal to be detected;
the orthogonal detection module comprises a first photoelectric detector, a radio frequency domain orthogonal demodulator, an instantaneous phase calculation unit and an instantaneous frequency calculation unit, wherein the local oscillation end of the radio frequency domain orthogonal demodulator is connected with a radio frequency source;
the first photoelectric detector is connected with the second coupler and used for receiving the laser signal to be detected, converting the laser signal to be detected into an electric signal to be detected and sending the electric signal to be detected to the signal end of the radio frequency domain quadrature demodulator;
the radio frequency domain quadrature demodulator is used for demodulating and outputting an I path signal and a Q path signal according to the electric signal to be detected;
the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In one embodiment, the delayed self-coherent module further comprises a polarization controller, and two ends of the polarization controller are respectively connected with the output end of the optical delay and the input end of the second coupler;
the orthogonal detection module further comprises two radio frequency filters, the input ends of the two radio frequency filters are respectively connected with the two output ends of the radio frequency domain orthogonal demodulator, and the output ends of the two radio frequency filters are respectively connected with the two input ends of the instantaneous phase calculation unit.
In one embodiment, the delayed self-coherent module comprises a third coupler, a 90 ° optical mixer and an optical retarder;
the third coupler is connected with the laser to be tested and is used for dividing the output laser signal of the laser to be tested into a first output laser signal and a second output laser signal;
the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change;
two input ends of the 90-degree optical mixer are respectively connected with the third coupler and the optical delayer so as to receive the first laser signal to be detected and the second output laser signal and output the laser signal to be detected according to the first laser signal to be detected and the second output laser signal, wherein the laser signal to be detected comprises the first laser signal and the second laser signal;
the orthogonal detection module comprises two second photodetectors, an instantaneous phase calculation unit and an instantaneous frequency calculation unit;
the two second photoelectric detectors are respectively connected with two output ends of the 90-degree optical mixer and used for respectively converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal;
the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In one embodiment, the delayed self-coherent module further comprises a polarization controller, and two ends of the polarization controller are respectively connected with the output end of the optical retarder and the input end of the 90 ° optical mixer;
the orthogonal detection module further comprises two radio frequency filters, the input ends of the two radio frequency filters are respectively connected with the output ends of the two second photoelectric detectors, and the output ends of the two radio frequency filters are respectively connected with the two input ends of the instantaneous phase calculation unit.
In one embodiment, the instantaneous phase calculation unit is used for obtaining the instantaneous phase of the output laser signal through a phase calculation formula according to the I path signal and the Q path signal;
the phase is calculated by the formula
Wherein, theta is the instantaneous phase, Q is the Q way signal, and I is the I way signal.
In one embodiment, the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to an instantaneous phase and frequency phase conversion formula;
the frequency-phase conversion formula is:
wherein f is the instantaneous frequency, and Δ τ is the relative delay time introduced by the optical delay between the first output laser signal and the second output laser signal;
the instantaneous frequency calculation unit is also used for calculating the actual instantaneous frequency of the laser to be measured according to the instantaneous frequency of the output laser signal and a preset formula;
the preset formula is as follows: f. of a ＝N·SR+，
Wherein the content of the first and second substances,
f a n is a non-negative integer for the actual instantaneous frequency.
In a second aspect, an embodiment of the present application provides a method for detecting a laser instantaneous frequency, where the method includes:
carrying out delay self-coherent processing on an output laser signal of a laser to be detected so as to enable the output laser signal to generate instantaneous phase change and obtain a laser signal to be detected containing the instantaneous phase change of the output laser signal;
and 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 according to the instantaneous phase.
In one embodiment, the performing a delayed self-coherent process on an output laser signal of a laser device under test to obtain a laser signal to be tested including an instantaneous phase change of the output laser signal includes:
dividing an output laser signal of a laser to be tested 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 delayer, and outputting the second output laser signal to an optical frequency shifter, wherein the optical frequency shifter is connected with a radio frequency source;
time delay is carried out on the first output laser signal through an optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained; frequency shifting is carried out on the second output laser signal through an optical frequency shifter according to the frequency of the radio frequency source, and a second laser signal to be tested containing frequency change is obtained;
the first laser signal to be detected and the second laser signal to be detected are re-coupled together through a second coupler to obtain a laser signal to be detected;
the orthogonal detection is carried out on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and the instantaneous frequency of the output laser signal is obtained through calculation according to the instantaneous phase, and the method comprises the following steps:
converting a laser signal to be detected into an electric signal to be detected through a first photoelectric detector, and sending the electric signal to be detected to a signal end of a radio frequency domain orthogonal demodulator, wherein a local oscillator end of the radio frequency domain orthogonal demodulator is connected with a radio frequency source;
demodulating and outputting an I path signal and a Q path signal according to the electric signal to be detected by a radio frequency domain quadrature demodulator;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In one embodiment, the performing a delayed self-coherent process on an output laser signal of a laser device under test to obtain a laser signal to be tested including an instantaneous phase change of the output laser signal includes:
dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal through a third coupler;
time delay is carried out on the first output laser signal through an optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained;
respectively inputting a first laser signal to be detected and a second output laser signal into two input ends of a 90-degree optical mixer so that the 90-degree optical mixer outputs the laser signal to be detected, wherein the laser signal to be detected comprises the first laser signal and the second laser signal;
the orthogonal detection is carried out on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and the instantaneous frequency of the output laser signal is obtained through calculation according to the instantaneous phase, and the method comprises the following steps:
converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal respectively through two second photodetectors;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In summary, compared with the prior art, the beneficial effects brought by the technical scheme provided by the embodiment of the application at least include:
according to the laser instantaneous frequency detection device provided by the embodiment of the application, the device can be connected with a laser to be detected through the delay self-coherent module so as to perform delay self-coherent processing on an output laser signal of the laser to be detected and obtain a laser signal to be detected containing instantaneous phase change of the output laser signal, the delay self-coherent module takes the detected signal as a reference source, an external reference source is not needed, and the complexity and the cost of a system are reduced; and then receiving the laser signal to be detected through an orthogonal detection module, carrying out 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 according to the instantaneous phase. The device adopts a frequency-phase conversion method, can utilize the natural linear relation between the frequency and the phase, and solves the fundamental problem of the nonlinearity of a frequency-intensity detection curve in the prior art, thereby avoiding introducing an external reference source, expanding a working area, eliminating a dead zone, avoiding the need of offsetting a working point, simplifying the complexity of a system, reducing the cost and improving the reliability of the system.
Drawings
Fig. 1 is a structural diagram of a laser instantaneous frequency detection device according to an embodiment of the present application.
Fig. 2 is a structural diagram of a laser instantaneous frequency detection device according to another embodiment of the present application.
Fig. 3 is a diagram illustrating a structure of a laser instantaneous frequency detection device according to another embodiment of the present application.
Fig. 4 is a structural diagram of a laser instantaneous frequency detection device according to still another embodiment of the present application.
Fig. 5 is a diagram illustrating a structure of a laser instantaneous frequency detection device according to another embodiment of the present application.
Fig. 6 is a flowchart of a laser instantaneous frequency detection method according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.
Referring to fig. 1, an embodiment of the present application provides a laser instantaneous frequency detection apparatus, including:
and the delayed self-coherent module 100 is connected with the laser to be detected, and is used for performing delayed self-coherent processing on the output laser signal of the laser to be detected to obtain the laser signal to be detected, which contains the instantaneous phase change of the output laser signal.
When the embodiment is used for laser sensing, the laser to be measured is a laser sensor carrying sensing information. At this time, the output laser signal of the laser device under test is the laser signal under test, and the frequency of the output laser signal can be regarded as the frequency of the laser sensor. The delayed self-coherent module 100 may be an integrated circuit that is composed of a plurality of devices, such as a coupler, an optical delay, an optical frequency shifter, and an optical mixer, which are commonly used in the prior art, and is capable of implementing delayed self-coherent processing of optical signals.
Specifically, the delayed self-coherent module 100 performs delayed self-coherent on the detected laser signal, so that the subsequent laser signal to be detected includes the instantaneous phase change of the detected laser signal; the delayed self-coherent module 100 is based on the self-coherent principle, and the measured signal is taken as a reference source, so that an external reference source is not needed, and the complexity and the cost of the system are reduced.
The orthogonal detection module 200, the orthogonal detection module 200 is connected to the delayed self-coherent module 100, and is configured to receive the laser signal to be detected, perform orthogonal detection on the laser signal to be detected, obtain an instantaneous phase of the output laser signal, and calculate an instantaneous frequency of the output laser signal according to the instantaneous phase.
The quadrature detection module 200 may be an integrated circuit or device that is composed of multiple modules, such as a photodetector, a phase calculation unit, and a frequency calculation unit, which are commonly used in the prior art, and that can implement an optical signal quadrature detection function, such as a commonly used radio frequency domain quadrature detection circuit and an optical domain quadrature detection circuit.
Specifically, the orthogonal detection module 200 may receive the laser signal to be detected from the delayed self-coherent module 100, perform orthogonal detection on the received laser signal to be detected, obtain an instantaneous phase of the laser signal to be detected because the delayed self-coherent module 100 has already caused the instantaneous phase change of the laser signal to be detected to be included in the laser signal to be detected by the delayed self-coherent module 100, and obtain a corresponding instantaneous frequency, that is, an instantaneous frequency of the output laser signal, from the instantaneous phase based on a frequency-phase linear relationship. Therefore, the instantaneous frequency variation of the laser signal to be measured can be obtained from the instantaneous phase variation by using the frequency-phase linear relationship. Because the linear relation can accurately measure the frequency change, after the linear relation of the frequency and the phase is adopted, the working point does not influence the measuring effect at any position, so that the working point is not needed to be biased, a complex bias point feedback control system is not needed to stabilize the bias point, the complexity and the cost of the system are reduced, and the reliability and the stability of the system are improved.
In the above embodiment, the device adopts a frequency-phase conversion method, and can solve the fundamental problem of non-linearity of a frequency-intensity detection curve in the prior art by using a natural linear relationship between frequency and phase, so that an external reference source is not required to be introduced, a working area is enlarged, a dead zone is eliminated, and a bias working point is not required, thereby reducing the complexity and cost of a system and improving the reliability of the system.
In some embodiments, please refer to an embodiment based on a heterodyne structure and radio frequency domain quadrature detection shown in fig. 2, the delayed self-coherent module 100 includes a first coupler, an optical frequency shifter, a second coupler, and an optical delay, wherein the optical frequency shifter is connected to a radio frequency source.
The first coupler is connected with the laser to be tested and used for dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal; the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change; the optical frequency shifter is used for shifting the frequency of the second output laser signal according to the frequency of the radio frequency source to obtain a second laser signal to be detected containing frequency change; the second coupler is used for re-coupling the first laser signal to be detected and the second laser signal to be detected together to obtain the laser signal to be detected.
In the delayed self-coherent module 100, the output laser signal of the laser to be tested is divided into two output signals by the first coupler: a first output laser signal and a second output laser signal. After the second output laser signal passes through the optical frequency shifter, the frequency of the second output laser signal is changed to obtain a second laser signal to be tested, and the frequency change amount is determined by the frequency of a radio frequency source driving the optical frequency shifter; the optical frequency shifter may be an acousto-optic modulator or other optoelectronic device capable of achieving similar functions. The first output laser signal passes through the optical delayer, so that a relative time delay relative to the second output laser signal passing through the optical frequency shifter is introduced, and a first laser signal to be detected is obtained. And finally, the two paths of signals are re-coupled together through a second coupler, and the laser signal to be detected is output.
The orthogonal detection module 200 includes a first photodetector, a radio frequency domain orthogonal demodulator, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit, where a local oscillation end of the radio frequency domain orthogonal demodulator is connected to a radio frequency source.
The first photoelectric detector is connected with the second coupler and used for receiving the laser signal to be detected, converting the laser signal to be detected into an electric signal to be detected and sending the electric signal to be detected to a signal end of the radio frequency domain orthogonal demodulator; the radio frequency domain quadrature demodulator is used for demodulating and outputting the I path signal and the Q path signal according to the electric signal to be detected; the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I path signal and the Q path signal; the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In the orthogonal 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, the electrical signal to be detected is sent to the signal end of the radio frequency domain orthogonal demodulator, and the local oscillator end of the radio frequency domain orthogonal demodulator is connected to the radio frequency source driving the optical frequency shifter, so that the radio frequency domain orthogonal demodulator demodulates the electrical signal to be detected and outputs two paths of signals, namely an I-path signal and a Q-path signal. And taking the I path signal and the Q path signal as the input of the instantaneous phase calculation unit, calculating to obtain the instantaneous phase of the laser to be measured, and converting the calculated instantaneous phase into the instantaneous frequency of the laser to be measured in the instantaneous frequency calculation unit.
In specific implementation, the analog-to-digital converter can be used for sampling and quantizing the signals of the I path and the Q path output by the radio frequency domain quadrature demodulator through analog-to-digital conversion, and then the signals are sent to the instantaneous phase calculation unit and the instantaneous frequency calculation unit for calculation to obtain the instantaneous frequency of the laser to be measured. The phase calculating unit and the frequency calculating unit may be implemented by commonly used calculating units in the prior art, such as a single chip, a DSP (Digital Signal Processing), an FPGA (Field Programmable Gate Array), a computer, and the like.
In the above embodiment, the apparatus may adopt the self-coherent delay module 100 including the coupler, the optical frequency shifter and the optical delay device, and the heterodyne radio frequency domain quadrature detection to implement the laser instantaneous frequency measurement, and utilize the natural linear relationship between the frequency and the phase without introducing an external reference source, thereby eliminating a dead zone and without biasing a working point.
In the actual application scene, optical amplifiers, electrical amplifiers, filters, polarization controllers, analog-to-digital converters and other devices for regulating and controlling optical or electrical signals can be added at appropriate places according to actual needs so as to improve indexes such as signal-to-noise ratio and obtain higher performance.
Based on the above embodiments, in some embodiments, as shown in fig. 3, the delayed self-coherent module 100 may further include a polarization controller, and two ends of the polarization controller are respectively connected to the output end of the optical retarder and the input end of the second coupler.
Specifically, the polarization controller is arranged on a branch of a first laser signal to be detected output by the optical retarder, and when the second coupler couples the first laser signal to be detected and a second laser signal to be detected together again, the polarization state of the polarization controller is adjusted, so that the polarization states of the two signals are optimally matched, the optical power output by the second coupler reaches the maximum value, and the signal-to-noise ratio is favorably improved.
The quadrature detection module 200 further includes two rf filters, wherein the input ends of the two rf filters are respectively connected to the two output ends of the rf domain quadrature demodulator, and the output ends of the two rf filters are respectively connected to the two input ends of the instantaneous phase calculation unit.
Wherein, the two rf filters may be the same rf band pass filter. Specifically, two output ends of the radio frequency domain quadrature demodulator respectively output an I-path signal and a Q-path signal, and the I-path signal and the Q-path signal both pass through the same radio frequency band-pass filter to filter out interference signals and out-of-band noise in the two paths of signals, thereby improving the detection accuracy.
In the above embodiment, the device can improve the signal-to-noise ratio by additionally arranging the polarization controller, and filter the I-path signal and the Q-path signal by arranging the radio frequency filter, so that the detection accuracy is improved.
In other embodiments, referring to an embodiment based on homodyne structure and optical domain quadrature detection shown in fig. 4, the delayed self-coherent module 100 includes a third coupler, a 90 ° optical mixer and an optical delay.
The third coupler is connected with the laser to be tested and used for dividing the output laser signal of the laser to be tested into a first output laser signal and a second output laser signal; the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change; two input ends of the 90-degree optical mixer are respectively connected with the third coupler and the optical delayer to receive the first laser signal to be detected and the second output laser signal and output the laser signal to be detected according to the first laser signal to be detected and the second output laser signal, wherein the laser signal to be detected comprises the first laser signal and the second laser signal.
In the delayed self-coherent module 100, the output laser signal of the laser to be tested is divided into two output signals by the first coupler: a first output laser signal and a second output laser signal. Wherein, the second output laser signal is input into the signal end of the 90-degree optical mixer; the first output laser signal passes through an optical delay to introduce a relative time delay with respect to the second output laser signal. And the optical delayer inputs the obtained first laser signal to be detected into a local oscillation end of the 90-degree optical mixer. The 90 ° optical mixer outputs a first laser signal and a second laser signal.
It should be noted that, the above-mentioned inputting the second output laser signal into the signal end of the 90 ° optical mixer and inputting the first laser signal to be measured into the local oscillator end of the 90 ° optical mixer is only for convenience of description, and in practical application, which of the 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 has no relationship, and the two branches may be interchanged without being affected.
The quadrature detection module 200 includes two second photodetectors, an instantaneous phase calculation unit, and an instantaneous frequency calculation unit.
The two second photoelectric detectors are respectively connected with two output ends of the 90-degree optical mixer and used for respectively converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal; the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I path signal and the Q path signal; the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
The two outputs of the 90-degree optical mixer are converted into electric signals by two second photodetectors, namely an I-path signal and a Q-path signal. The I path signal and the Q path signal are used as the input of the instantaneous phase calculation unit, and the instantaneous phase of the laser to be measured is obtained after calculation. The calculated instantaneous phase is then converted to the instantaneous frequency of the laser under test in an instantaneous frequency calculation unit.
In the above embodiment, the apparatus may adopt the self-coherent delay module 100 including a coupler, a 90 ° optical mixer and an optical retarder, and the homodyne optical domain quadrature detection to realize the laser instantaneous frequency measurement, and utilize the natural linear relationship between the frequency and the phase without introducing an external reference source, thereby eliminating a dead zone and without biasing the operating point.
Based on the above embodiments, in some embodiments, as shown in fig. 5, the delayed self-coherent module 100 may further include a polarization controller, and two ends of the polarization controller are respectively connected to the output end of the optical retarder and the input end of the 90 ° optical mixer.
During specific implementation, the polarization state of the polarization controller is adjusted, so that the polarization states of two paths of signals entering the 90-degree optical mixer are optimally matched, the optical power output by the 90-degree optical mixer reaches the maximum value, and the signal-to-noise ratio of the embodiment is improved.
The quadrature detection module 200 may further include two rf filters, wherein input ends of the two rf filters are respectively connected to output ends of the two second photodetectors, and output ends of the two rf filters are respectively connected to two input ends of the instantaneous phase calculation unit.
Wherein, the two rf filters may be the same rf low pass filter. Specifically, two output ends of the radio frequency domain quadrature demodulator respectively output an I path signal and a Q path signal, and the I path signal and the Q path signal pass through the same radio frequency low pass filter to filter out interference signals and out-of-band noise in the two paths of signals, so that the detection accuracy is improved.
In the above embodiment, the device can improve the signal-to-noise ratio by adding the polarization controller, and filter the I path signal and the Q path signal by setting the radio frequency filter, thereby improving the detection accuracy.
In some embodiments, the instantaneous phase calculation unit is configured to obtain the instantaneous phase of the output laser signal according to the I-path signal and the Q-path signal through a phase calculation formula. Specifically, the instantaneous phase calculation unit has two input signals: the I path signal and the Q path signal can be respectively marked as I and Q, and are calculated by a phase calculation formula
The instantaneous phase θ can be calculated.
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 Δ τ, based on the linear relationship between frequency and phase, the instantaneous frequency calculation unit may convert the instantaneous frequency into the frequency-phase conversion formula
And calculating the instantaneous frequency f of the laser to be measured.
In practical applications, the calculated instantaneous frequency f is not necessarily equal to the actual instantaneous frequency of the laser under test. Let us say that the actual instantaneous frequency of the laser under test is recorded as f a Then f is a The relationship with f is as follows: f. of a = FSR + f, where FSR (Free Spectral Range) may be referred to as Free Spectral width, inversely proportional to the relative delay time introduced by the optical retarder, i.e. the optical retarder
Wherein N is a non-negative integer.
Therefore, the working area of the laser instantaneous frequency detection device in the embodiment is an FSR. Since in sensing applications only the change in instantaneous frequency f is of interest, N is not of interest. Thus, different laser frequencies, according to the formula f a The calculation of N · SR + automatically yields different N (and f)<FSR) to automatically adapt the long-term stable operating frequency of the laser. When the instantaneous frequency of the laser changes by no more than an FSR range, N does not change and the calculated change in the instantaneous frequency f of the laser reflects the change in the actual instantaneous frequency fa of the laser.
It should be noted that the specific location of the working region on the frequency spectrum is adaptive, i.e. the long-term stable operating frequency of the laser is automatically adapted, and the calculated instantaneous frequency f fluctuates around the long-term stable operating frequency, so that no offset point needs to be set. In practical application, the size of the working area range of the system can be adjusted by adjusting the relative delay time introduced by the optical delayer. The device in the embodiment is a linear working region in the whole free spectral width range (FSR), and the operable frequency domain is greatly widened, so that the system has a larger dynamic range.
The modules in the laser instantaneous frequency detection device can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
The devices related in the above embodiments may be replaced by devices having similar functions, for example, multiple devices are integrated into one device by a process means such as photoelectric integration, so as to achieve the purpose of reducing cost. None of these approaches is directed to the fundamental changes in the principles presented herein and should be considered within the scope of this application.
Referring to fig. 6, an embodiment of the present application provides a method for detecting a laser instantaneous frequency, which may include the following steps:
step S1, delay self-coherent processing is carried out on an output laser signal of a laser to be detected, and the laser signal to be detected containing instantaneous phase change of the output laser signal is obtained.
Specifically, the output laser signal of the laser to be detected is subjected to delayed self-coherent processing, so that the output laser signal is compared with the phase of the output laser signal in a past period of time to obtain the laser signal to be detected containing the instantaneous phase change of the output laser signal.
And S2, 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 according to the instantaneous phase.
In the embodiment, the method can solve the fundamental problem of the nonlinearity of the frequency-intensity detection curve in the prior art by utilizing the natural linear relation between the frequency and the phase, so that an external reference source is not required to be introduced, the working area is enlarged, the dead zone is eliminated, and the offset working point is not required any more, thereby reducing the complexity and the cost of the system and improving the reliability of the system.
In some embodiments, step S1 may comprise the steps of:
dividing an output laser signal of a laser to be tested 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 delayer, and outputting the second output laser signal to an optical frequency shifter, wherein the optical frequency shifter is connected with a radio frequency source;
time delay is carried out on the first output laser signal through an optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained; frequency shifting is carried out on the second output laser signal through an optical frequency shifter according to the frequency of the radio frequency source, and a second laser signal to be tested containing frequency change is obtained;
the first laser signal to be detected and the second laser signal to be detected are re-coupled together through a second coupler to obtain a laser signal to be detected;
step S2 may comprise the steps of:
converting a laser signal to be detected into an electric signal to be detected through a first photoelectric detector, and sending the electric signal to be detected to a signal end of a radio frequency domain orthogonal demodulator, wherein a local oscillator end of the radio frequency domain orthogonal demodulator is connected with a radio frequency source;
demodulating and outputting an I path signal and a Q path signal according to the electric signal to be detected by a radio frequency domain quadrature demodulator;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
In other embodiments, step S1 may include the steps of:
dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal through a third coupler;
time delay is carried out on the first output laser signal through an optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained;
respectively inputting a first laser signal to be detected and a second output laser signal into two input ends of a 90-degree optical mixer so that the 90-degree optical mixer outputs the laser signal to be detected, wherein the laser signal to be detected comprises the first laser signal and the second laser signal;
step S2 may comprise the steps of:
converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal respectively through two second photodetectors;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
For specific limitations of the laser instantaneous frequency detection method provided in the foregoing embodiments, reference may be made to the foregoing embodiments of the laser instantaneous frequency detection device, and details are not described herein again.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. 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. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), rambus (Rambus) direct RAM (RDRAM), direct Rambus Dynamic RAM (DRDRAM), and Rambus Dynamic RAM (RDRAM), among others.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.
Claims (10)
1. A laser instantaneous frequency detection apparatus, characterized in that the apparatus comprises:
the delay self-coherent module is connected with the laser to be detected and is used for carrying out delay self-coherent processing on the output laser signal of the laser to be detected so as to obtain the laser signal to be detected containing the instantaneous phase change of the output laser signal;
the orthogonal detection module is connected with the delayed self-coherent module and used for receiving the laser signal to be detected, carrying out 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 according to the instantaneous phase.
2. The apparatus of claim 1, wherein the delayed self-coherent module comprises a first coupler, an optical frequency shifter, a second coupler and an optical delay device, the optical frequency shifter is connected to a radio frequency source;
the first coupler is connected with the laser to be tested and used for dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal;
the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change;
the optical frequency shifter is used for shifting the frequency of the second output laser signal according to the frequency of the radio frequency source to obtain a second laser signal to be detected containing frequency change;
the second coupler is used for re-coupling the first laser signal to be detected and the second laser signal to be detected together to obtain the laser signal to be detected;
the orthogonal detection module comprises a first photoelectric detector, a radio frequency domain orthogonal demodulator, an instantaneous phase calculation unit and an instantaneous frequency calculation unit, wherein the local oscillation end of the radio frequency domain orthogonal demodulator is connected with the radio frequency source;
the first photoelectric detector is connected with the second coupler and used for receiving the laser signal to be detected, converting the laser signal to be detected into an electric signal to be detected and sending the electric signal to be detected to a signal end of the radio frequency domain orthogonal demodulator;
the radio frequency domain quadrature demodulator is used for demodulating and outputting an I path signal and a Q path signal according to the electric signal to be detected;
the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
3. The apparatus of claim 2, wherein the delayed self-coherent module further comprises a polarization controller, and both ends of the polarization controller are respectively connected to the output end of the optical retarder and the input end of the second coupler;
the orthogonal detection module further comprises two radio frequency filters, the input ends of the two radio frequency filters are respectively connected with the two output ends of the radio frequency domain orthogonal demodulator, and the output ends of the two radio frequency filters are respectively connected with the two input ends of the instantaneous phase calculation unit.
4. The apparatus of claim 1, wherein the delayed self-coherent module comprises a third coupler, a 90 ° optical mixer, and an optical delay;
the third coupler is connected with the laser to be tested and is used for dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal;
the optical delayer is used for carrying out time delay on the first output laser signal to obtain a first laser signal to be detected containing instantaneous phase change;
two input ends of the 90-degree optical mixer are respectively connected with the third coupler and the optical delayer to receive the first laser signal to be detected and the second output laser signal and output the laser signal to be detected according to the first laser signal to be detected and the second output laser signal, wherein the laser signal to be detected comprises the first laser signal and the second laser signal;
the orthogonal detection module comprises two second photoelectric detectors, an instantaneous phase calculation unit and an instantaneous frequency calculation unit;
the two second photodetectors are respectively connected with two output ends of the 90-degree optical mixer and are used for respectively converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal;
the instantaneous phase calculation unit is used for calculating the instantaneous phase of the output laser signal according to the I-path signal and the Q-path signal;
the instantaneous frequency calculation unit is used for calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
5. The apparatus of claim 4, wherein the delayed self-coherent module further comprises a polarization controller, and both ends of the polarization controller are respectively connected to the output end of the optical retarder and the input end of the 90 ° optical mixer;
the orthogonal detection module further comprises two radio frequency filters, the input ends of the two radio frequency filters are respectively connected with the output ends of the two second photoelectric detectors, and the output ends of the two radio frequency filters are respectively connected with the two input ends of the instantaneous phase calculation unit.
6. The apparatus according to any one of claims 2 to 5, wherein the instantaneous phase calculation unit is configured to obtain an instantaneous phase of the output laser signal according to the I-path signal and the Q-path signal by a phase calculation formula;
the phase calculation formula is
And theta is the instantaneous phase, Q is the Q path signal, and I is the I path signal.
7. The apparatus of claim 6, wherein the instantaneous frequency calculation unit is configured to calculate an instantaneous frequency of the output laser signal according to the instantaneous phase and frequency phase conversion formula;
the frequency-phase conversion formula is as follows:
wherein f is the instantaneous frequency and Δ τ is the relative delay time introduced by the optical delay between the first output laser signal and the second output laser signal;
the instantaneous frequency calculation unit is also used for calculating the actual instantaneous frequency of the laser to be measured according to the instantaneous frequency of the output laser signal and a preset formula;
the preset formula is as follows: f. of a ＝N·SR+，
Wherein the content of the first and second substances,
f a for the actual instantaneous frequency, N is a non-negative integer.
8. A method of laser instantaneous frequency detection, the method comprising:
carrying out delayed self-coherent processing on an output laser signal of a laser to be detected to obtain a laser signal to be detected containing instantaneous phase change of the output laser signal;
and carrying out 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 according to the instantaneous phase.
9. The method of claim 8, wherein the delaying self-coherent processing of the output laser signal of the laser under test to obtain the laser signal to be tested including the instantaneous phase change of the output laser signal comprises:
dividing an output laser signal of the laser to be tested 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 delayer, and outputting the second output laser signal to an optical frequency shifter, wherein the optical frequency shifter is connected with a radio frequency source;
time delay is carried out on the first output laser signal through the optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained; frequency shifting is carried out on the second output laser signal through the optical frequency shifter according to the frequency of the radio frequency source, and a second laser signal to be tested containing frequency change is obtained;
the first laser signal to be detected and the second laser signal to be detected are re-coupled together through a second coupler to obtain the laser signal to be detected;
the orthogonal detection is performed on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and the instantaneous frequency of the output laser signal is calculated according to the instantaneous phase, and the method comprises the following steps:
converting the laser signal to be detected into an electric signal to be detected through a first photoelectric detector, and sending the electric signal to be detected to a signal end of a radio frequency domain orthogonal demodulator, wherein a local oscillator end of the radio frequency domain orthogonal demodulator is connected with a radio frequency source;
demodulating and outputting an I path signal and a Q path signal according to the electric signal to be detected through the radio frequency domain quadrature demodulator;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
10. The method of claim 8, wherein the delaying self-coherent processing of the output laser signal of the laser under test to obtain the laser signal to be tested including the instantaneous phase change of the output laser signal comprises:
dividing an output laser signal of the laser to be tested into a first output laser signal and a second output laser signal through a third coupler;
time delay is carried out on the first output laser signal through an optical delayer, and a first laser signal to be detected containing instantaneous phase change is obtained;
inputting the first laser signal to be detected and the second output laser signal into two input ends of a 90-degree optical mixer respectively, so that the 90-degree optical mixer outputs the laser signal to be detected, wherein the laser signal to be detected comprises a first laser signal and a second laser signal;
the orthogonal detection is performed on the laser signal to be detected to obtain the instantaneous phase of the output laser signal, and the instantaneous frequency of the output laser signal is calculated according to the instantaneous phase, and the method comprises the following steps:
converting the first laser signal and the second laser signal into an I-path signal and a Q-path signal respectively through two second photodetectors;
calculating to obtain the instantaneous phase of the output laser signal according to the I path signal and the Q path signal;
and calculating the instantaneous frequency of the output laser signal according to the instantaneous phase.
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