Disclosure of Invention
The invention aims to provide a plant ecology monitoring system based on an optical frequency comb, which utilizes a femtosecond optical frequency comb with determined repetition frequency difference as a monitoring light source, converts optical frequency information into radio frequency information for detection under the condition of beat frequency with reference light after the monitoring light collects optical signals of a monitored object, and carries out high-speed collection, calculation and reduction, and inverts an absorption spectrum of the optical frequency from the radio frequency information to obtain spectral information of the monitored object, and inverts phase information of the optical frequency to invert the space relative position of the monitored object and realize three-dimensional imaging.
The purpose of the invention is realized by the following technical scheme:
a plant ecology monitoring system based on optical frequency comb is characterized by comprising an optical frequency comb light source module, an optical monitoring module, a detector module, a data acquisition and processing module and a clock synchronization module, wherein two output ends of the optical frequency comb light source module are respectively connected with input ends of the optical monitoring module and the detector module, the output end of the optical monitoring module is connected with the input end of the detector module, the output end of the detector module is connected with the input end of the data acquisition and processing module, and two output ends of the clock synchronization module are respectively connected with the input end of the optical frequency comb light source module and the input end of the data acquisition and processing module;
the optical frequency comb light source module outputs monitoring light and reference light with a frequency repetition difference, the monitoring light acts on a monitoring object after the power, the wavelength and the light beam of the monitoring light are adjusted by the optical monitoring module, the detector module receives the monitoring light reflected by the monitoring object, the detector module carries out beat frequency on the returned monitoring light and the reference light, and the data acquisition and processing module acquires beat frequency signals sent by the detector module and then analyzes and restores the absorption spectrum and the morphological characteristics of the monitoring object in real time.
The optical frequency comb light source module comprises two femtosecond optical frequency combs with a frequency re-difference and a locking module for realizing the frequency re-difference, wherein the locking mode of the frequency re-difference is one or more of optical frequency reference locking, carrier envelope zero frequency locking and frequency re-locking.
The feedback excitation of the locking mode of the weight frequency difference is one or a combination of more of piezoelectric ceramics, current, temperature, an electro-optic modulation crystal, a saturable absorber, a carbon nano tube and a graphene modulator.
The wavelength ranges of the two optical frequency combs are in the wavelength ranges of extreme ultraviolet, visible light, near infrared, intermediate infrared and far infrared.
The optical monitoring module is composed of a virtual imaging phase array, a grating and a telescope system, the virtual imaging phase array and the grating are used for carrying out area array arrangement on light source signals, and the telescope system is used for adjusting the size of light spots incident on the monitored object.
The optical monitoring module comprises a half wave plate, a first polarization beam splitter, a quarter wave plate, a virtual imaging phase array, a grating, a first confocal lens and a second confocal lens which are sequentially arranged.
The detector module comprises a half wave plate, a second polarization beam splitter, a half wave plate, a third polarization beam splitter and a detector which are arranged in sequence.
The detector is one or a combination of a photodiode detector, a single photon detector and an optical balance detector.
The clock synchronization module is one of an atomic clock, an optical clock and a signal generator.
The invention has the advantages that: (1) the plant ecological monitoring system is based on the principle of optical frequency comb beat frequency detection, monitoring light reflected by a monitored object and reference light are subjected to beat frequency down-conversion to a radio frequency wave band through two femtosecond lasers with determined repeat frequency difference, a down-conversion signal is directly detected by using a photoelectric detector, optical frequency information can be accurately inverted, the refreshing time of the system is determined by the repeat frequency difference, the refreshing time reaches the sub-ms magnitude, the measuring speed is extremely high, and instant measurement can be realized. (2) The plant ecology monitoring system inverts and restores the phase of the optical frequency through the detected radio frequency information, so that the three-dimensional structure of a monitored object is analyzed, the accuracy of the analysis depth can reach the nm magnitude, and high-accuracy measurement is realized. (3) The plant ecology monitoring system adopts the optical frequency comb system with the all-fiber structure, can realize the integration, simplification and miniaturization of the detection system, and has simple installation and simple and convenient operation. (4) The plant ecology monitoring system is used for inverting the optical frequency signal of the monitored object by detecting the time domain signal of the beat frequency signal, analyzing the three-dimensional appearance of the monitored object by a phase method while analyzing the absorption spectrum information, and realizing the simultaneous measurement of the three-dimensional appearance and the spectrum signal by only one detector.
Detailed Description
The features of the present invention and other related features are described in further detail below by way of example in conjunction with the following drawings to facilitate understanding by those skilled in the art:
as shown in fig. 1-2, the respective symbols in the figure are: the optical frequency comb light source module 1, the optical monitoring module 2, the detector module 3, the data acquisition and processing module 4, the clock synchronization module 5, the monitored object 6, the first optical frequency comb 11, the second optical frequency comb 12, the locking module 13, the half wave plate a 21, the first polarization beam splitter 22, the quarter wave plate 23, the virtual imaging phase array 24, the grating 25, the first confocal lens 26, the second confocal lens 27, the half wave plate B31, the second polarization beam splitter 32, the half wave plate C33, the third polarization beam splitter 34, the optical balance detector 35, the data acquisition card 41 and the computing system 42.
Example (b): as shown in fig. 1 and 2, this embodiment concretely relates to plant ecological monitoring system based on optical frequency comb, this plant ecological monitoring system includes optical frequency comb light source module 1, optical monitoring module 2, detector module 3, data acquisition and processing module 4 and clock synchronization module 5, two outputs of optical frequency comb light source module 1 link to each other with optical monitoring module 2's input and detector module 3's input respectively, optical monitoring module 2's output links to each other with detector module 3's input, detector module 3's output then links to each other with data acquisition and processing module 4, and two outputs of clock synchronization module 5 link to each other with optical frequency comb light source module 1's input and data acquisition and processing module 4's input respectively.
As shown in fig. 1 and 2, the optical frequency comb light source module 1 outputs monitoring light for monitoring and reference light for beat frequency detection, and includes two optical frequency combs whose repetition frequency difference is 1kHz and a locking module 13, the central wavelengths of laser pulses generated by the two optical frequency combs are 1560nm, the two optical frequency combs are respectively recorded as a first optical frequency comb 11 and a second optical frequency comb 12, the locking module 13 is composed of two narrow linewidth lasers, and the locking manner of the repetition frequency difference includes, but is not limited to, optical frequency reference locking (i.e., beat frequency locking with the narrow linewidth continuous laser), carrier envelope zero frequency locking (i.e., carrier envelope zero frequency locking of the optical frequency combs), and repetition frequency locking (i.e., repetition frequency locking of the optical frequency combs), and the locking module 13 in this embodiment adopts optical frequency reference locking, i.e., beat frequency locking of the narrow linewidth continuous lasers. It should be noted that the feedback excitation of the optical-frequency comb locking manner includes, but is not limited to: piezoelectric ceramic, current, temperature, electro-optic modulation crystal, saturable absorber, carbon nanotube and graphene modulator; the wavelengths of the first optical-frequency comb 11 and the second optical-frequency comb 12 include, but are not limited to: extreme ultraviolet, visible light, near infrared, mid infrared, and far infrared.
As shown in fig. 1 and 2, the optical monitoring module 2 is configured to adjust characteristics of power, wavelength, and light beam of the monitoring light of the optical frequency comb light source module 1, and apply the characteristics to the monitored object 6, and includes a virtual imaging phase array 24, a grating 25, and a telescope system, and specifically includes a half-wave plate a 21, a first polarization beam splitter 22, a quarter-wave plate 23, a virtual imaging phase array 24, a grating 25, a first confocal lens 26, and a second confocal lens 27, which are sequentially arranged, where the virtual imaging phase array 24 and the grating 25 perform area array arrangement on the light source signal according to the size of the optical frequency, and the telescope system adjusts the size of the light spot incident on the monitored object 6.
As shown in fig. 1 and 2, the detector module 3 directly receives the monitoring light reflected by the monitoring object 6 and connects with the reference light of the optical frequency comb light source module 1 to realize beat frequency detection of the return monitoring light and the reference light; the detector module 3 includes a half-wave plate B31, a second polarization beam splitter 32, a half-wave plate C33, a third polarization beam splitter 34, and an optical balance detector 35, which are sequentially disposed, wherein the optical balance detector 35 may also adopt a photodiode detector and a single photon detector.
As shown in fig. 1 and 2, the data collecting and processing module 4 is responsible for collecting and processing the detected beat frequency signal at a high speed, and reducing the three-dimensional morphology information and the spectrum information of the monitored object 6 in real time, and includes a data collecting card 41 and a computing system 42.
As shown in fig. 1 and 2, the clock synchronization module 5 is connected to the optical frequency comb light source module 1 and the data acquisition and processing module 4, and synchronously triggers the time domain correlation module to reduce monitoring errors and implement high-precision morphology imaging and spectral analysis, and the clock synchronization module 5 is one of an atomic clock, an optical clock and a signal generator.
As shown in fig. 2, the working method of the plant ecology monitoring system based on the optical frequency comb in this embodiment is as follows:
(1) the first optical frequency comb 11 and the second optical frequency comb 12 generate laser pulses at the same time, and two narrow linewidth lasers with wavelengths of 1540nm and 1580nm in the locking module 13 respectively lock comb teeth of the first optical frequency comb 11 and comb teeth of the second optical frequency comb 12, so that accurate repetition frequency difference of 1kHz is realized;
(2) the first optical frequency comb 1 inputs monitoring light into the optical monitoring module 2, the monitoring light is adjusted in polarization state through a half-wave plate A21, a first polarization beam splitter 22 and a quarter-wave plate 23 in sequence, different optical frequency components are expanded according to spatial positions through a virtual imaging phase array 24 and a grating 25, then the light beam is expanded to cover the monitored object 6 through a telescope system formed by a first confocal lens 26 and a second confocal lens 27, the light emitted by the monitored object 6 is reflected through a second polarization beam splitter 32 and returned from an original path, polarization state conversion is realized under the action of the quarter-wave plate 23, and the light enters the detector module 3;
(3) meanwhile, the second optical frequency comb 12 outputs reference light, the reference light passes through a half-wave plate B31 and passes through the second polarization beam splitter 32 and the monitoring light, the polarization state of the combined light is adjusted through a half-wave plate C33, so that the monitoring light and the detection light can be equally divided by the third polarization beam splitter 34 at the same time, and the equally divided two paths of light are input into the optical balance detector 35 for photoelectric detection;
(4) the electrical signal output by the detector module 3 is received by the data acquisition and processing module 4, the data is acquired by the data acquisition card 41, the data is processed by the computing system 42, the morphology information and the spectrum information of the monitored object are restored, and the whole plant ecology monitoring system is synchronized by the signal of the rubidium atomic clock in the synchronous clock module 5.
In this embodiment, two optical frequency combs of the optical frequency comb light source module 1 are locked by two narrow linewidth lasers at the same time, the positions of the comb teeth are relatively fixed, the repetition frequency difference is kept at 1kHz, the optical balance detector 35 detects a beat frequency time domain signal with a period of 1ms, the sampling rate of the data acquisition card 41 is 100MHz, the time domain signal within 1ms is subjected to fourier transform, spectrum information can be obtained, so as to determine the gas components in the current environment of a plant, and similarly, the relative positions of points in a plant space can be calculated by analyzing phase information of different optical frequency components, so as to restore the three-dimensional shape state of the plant, and realize simultaneous measurement of the spectrum and the shape.