CN119245829A - A passive laser heterodyne double-balanced spectrum detection method and device - Google Patents
A passive laser heterodyne double-balanced spectrum detection method and device Download PDFInfo
- Publication number
- CN119245829A CN119245829A CN202411787051.3A CN202411787051A CN119245829A CN 119245829 A CN119245829 A CN 119245829A CN 202411787051 A CN202411787051 A CN 202411787051A CN 119245829 A CN119245829 A CN 119245829A
- Authority
- CN
- China
- Prior art keywords
- signal
- convex lens
- target
- signals
- light
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- General Physics & Mathematics (AREA)
- Optical Communication System (AREA)
Abstract
本发明涉及光谱探测技术领域，具体提供一种被动的激光外差双平衡光谱探测方法及装置，使用光混频器和光电二极管，对输入的窄线宽激光本振信号和宽谱的非相干目标光信号进行混频和差分处理，产生两路相位相差90°的随机时间拍频光电流信号，该随机时间拍频光电流信号包含信号光的光谱等信息，对输出的光电流信号进行滤波、积分等方法进行处理可以恢复信号光的光谱信息，利用这种方法，可以利用窄线宽激光本振信号的窄线宽及波长可调谐特性对宽谱非相干光信号进行高光谱分辨率信息获取，并有效提高本振光的利用效率，消除共模噪声和部分系统噪声，增强了输出信号的信噪比。
The present invention relates to the technical field of spectrum detection, and specifically provides a passive laser heterodyne double-balanced spectrum detection method and device. An optical mixer and a photodiode are used to mix and differentially process an input narrow-linewidth laser local oscillator signal and a wide-spectrum incoherent target optical signal, so as to generate two random time beat frequency photocurrent signals with a phase difference of 90°. The random time beat frequency photocurrent signal contains information such as the spectrum of the signal light. The output photocurrent signal is processed by filtering, integrating and other methods to restore the spectrum information of the signal light. By using this method, the narrow linewidth and wavelength tunable characteristics of the narrow-linewidth laser local oscillator signal can be used to obtain high spectral resolution information of the wide-spectrum incoherent optical signal, and the utilization efficiency of the local oscillator light is effectively improved, the common mode noise and part of the system noise are eliminated, and the signal-to-noise ratio of the output signal is enhanced.
Description
Technical Field
The invention relates to the technical field of spectrum detection, and particularly provides a passive laser heterodyne double-balance spectrum detection method and device.
Background
The basic principle of the laser heterodyne detection technology is that a beam of local oscillation light with high power, narrow laser linewidth and adjustable frequency is introduced to be mixed and overlapped with incident signal light on a photosensitive surface, and a photoelectric conversion device and a filter device are utilized to convert the frequency magnitude into the frequency magnitudeIs converted to an infrared signal of (2)The heterodyne radio frequency signal is processed to obtain the information such as the spectrum, the frequency and the like of the signal light.
One of the core advantages of the laser heterodyne detection technology is that the high-sensitivity amplification effect of weak signals is realized. Specifically, when the power of the local oscillation light is adjusted to a higher level, the local oscillation light can be used as a carrier wave to effectively amplify the weak signal. In practical application, through carefully designed system parameters, the strength of the heterodyne signal finally generated can be improved by several orders of magnitude compared with that of the original signal light, and can reach 6 to 9 orders of magnitude generally. The dynamic range of signal detection is greatly expanded, the influence of noise on signals is obviously reduced, and accurate and reliable signal extraction and analysis can be realized even under extremely weak or complex interference environments.
Another core advantage of the laser heterodyne detection technique is represented by its efficient frequency selectivity, which only responds to and processes the difference frequency signal that strictly meets its preset detectable bandwidth limit, thus realizing accurate screening and identification of the frequency components of the signal. In other words, only when the difference between the frequency of the signal light and the frequency of the local oscillator light is just within the preset bandwidth of the system, the difference frequency signal generated by the interaction of the two signals can be effectively identified and responded. Otherwise, if the frequency difference exceeds the bandwidth limit of the system, the corresponding heterodyne signal will not be captured by the system, thereby achieving automatic rejection of extraneous frequency components. The mechanism endows the laser heterodyne detection technology with natural filtering performance, eliminates stray light interference without relying on a complex narrow-band filter like the direct detection technology, greatly simplifies the complexity of the system and improves the accuracy and reliability of detection.
With the development of semiconductor technology and laser technology, the laser heterodyne technology is gradually applied to the field of spectroscopy with the advantages of high environmental adaptability, high spatial resolution, high spectral resolution and the like. For example, the Chinese academy of sciences of fertilizer-closing substance science, talking about pictures, and the like develop an all-fiber laser heterodyne solar radiometer which can measure solar spectrum data with high spectrum resolution in real time, and has the advantages of small volume, convenient use and the like. The radiometer is connected with a solar tracker, an optical fiber, a high-speed heterodyne detector, a radio frequency processor and other components, and is combined with a tunable narrow linewidth laser, so that heterodyne signal acquisition with high signal to noise ratio can be realized, and local oscillation light and real-time output wavelength information thereof can be conveniently provided. Andelu sapel et al invented a new combustion efficiency monitoring apparatus and method of operating the same. The device utilizes a laser heterodyne technology, light emitted by a combustion zone is captured and mixed with a local oscillation signal to generate photocurrent, and a difference frequency signal proportional to the concentration of a target substance is separated through filtering, so that the combustion efficiency is monitored in real time.
Although the conventional heterodyne detection technique plays a fundamental role in many optical signal detection scenarios, its inherent limitations are increasingly prominent. Specifically, one of the disadvantages of this technique is that the power of the local oscillation light is not fully utilized, and the noise influence is large. The local oscillation light is used as a key link in heterodyne detection, and the effective utilization of the power of the local oscillation light directly relates to the sensitivity and the precision of detection. In the traditional heterodyne detection, the loss of light waves in the transmission process and the deficiency of a power distribution mechanism often lead to insufficient utilization of local oscillation optical power. In the practical application process, the environment is complex and changeable, and the influence of noise is increased. These noise sources include, but are not limited to, thermal noise, shot noise, and various electronic and mechanical noise within the system. These noise components are interleaved with the target signal, which is difficult to resolve by conventional heterodyne detection techniques, resulting in a reduction in signal-to-noise ratio. Therefore, when high-precision measurement or weak signal detection is performed, the traditional heterodyne detection causes energy waste and detection efficiency reduction, and the sensitivity is severely restricted, so that the improvement of detection performance is affected.
In addition, the core of the laser heterodyne spectrum detection technology is to obtain the difference frequency component of the target signal and the local oscillation signal, so that the stability of the local oscillation signal is high. In particular, its stability is directly related to the accuracy of the detection result. In practical applications, the stability of the local oscillator signal is very susceptible to interference from a variety of factors. External environmental factors, such as minor fluctuations in ambient temperature, vibrations of mechanical structures, or interference of electromagnetic fields, may act on the laser by physical effects, resulting in unpredictable variations in the frequency, phase, or intensity of the output light wave. Additional disturbances are also introduced by system internal factors such as noise of electronic devices, aging of lasers, and minor imperfections in the optical path design, further affecting the stability of the local oscillator signal. Once the interference factors act on the local oscillation signals, the phase locking relation between the local oscillation signals and the target signals is destroyed, and phase errors and amplitude fluctuation in the process of extracting the difference frequency components are caused. These errors not only reduce the signal-to-noise ratio of the detected signal, but may distort the true morphology of the spectral features, so that the final detected result deviates from the true value, thereby affecting the accuracy and reliability of the data analysis.
Disclosure of Invention
The invention provides a passive laser heterodyne double-balance spectrum detection method and a device thereof, which not only improve the signal to noise ratio of a detection system, but also ensure that the system can still maintain higher detection precision and stability under the condition of fluctuation of the stability of local oscillation light, thereby obviously reducing the requirement on the stability of the local oscillation light.
In a first aspect, the present invention provides a passive laser heterodyne double balanced spectrum detection method, including:
Collecting a target optical signal by using an optical system, wherein the target optical signal is broad-spectrum incoherent light and consists of optical signals with different frequencies, and the complex amplitudes of the optical signals with different frequencies are random functions related to time;
The method comprises the steps of carrying out chopper modulation on a target optical signal by utilizing a chopper, inputting the modulated target optical signal to a target signal input end of an optical mixer, inputting a narrow linewidth laser local oscillation signal to a local oscillation input end of the optical mixer, wherein in the optical mixer, the target optical signal and the narrow linewidth laser local oscillation signal are overlapped, the overlapped target optical signal comprises a direct current part and an alternating current part, wherein a part with the frequency magnitude exceeding the record limit of a photoelectric detector is the direct current part, coherent overlapping is carried out according to the part, close to the frequency of the narrow linewidth laser local oscillation signal, in the target optical signal, of the components, which are detected by the photoelectric detector are called alternating current signals, the optical mixer outputs four paths of photocurrent signals, each path of signals comprises a direct current part and an alternating current part, wherein the direct current part is proportional to the light intensity sum of the narrow linewidth laser signal and the target optical signal, and the relative local oscillation phase difference exists between the alternating current parts, and the relative local oscillation phase difference is 0 respectively 、90、180And 270;
Selecting a proper filtering range to carry out band-pass filtering on four paths of output, inputting two paths of signals of 0 degree and 180 degrees into a pair of photodiodes, carrying out differential processing on the output of the photodiodes, enabling the output electric signals to be called in-phase signals, inputting two paths of signals of 90 degrees and 270 degrees into another pair of photodiodes, and outputting two paths of signals of 90 degrees and 270 degrees into quadrature signals, wherein the in-phase signals and the quadrature signals are twice of an alternating current part of the input signals, and do not contain a direct current part, and the in-phase signals and the quadrature signals have 90-degree phase delay;
And carrying out harmonic detection on the in-phase signal and the quadrature signal through a phase-locked amplifier, wherein a reference signal of the phase-locked amplifier is from the frequency of a chopper, inputting the two paths of signals into an oscilloscope for sampling, squaring and summing the amplitudes of the two paths of signals acquired by the oscilloscope, obtaining a result proportional to the target optical signal intensity at the current moment, obtaining the target optical signal intensity in a preset time, obtaining a calculated average value of the target optical signal intensity in the preset time, and obtaining the light intensity information with high spectral resolution.
As a preferred embodiment, the collecting the target optical signal by using the optical system includes:
The method comprises the steps that a target optical signal is converged at a rear focal point of a first convex lens through the first convex lens, a first concave lens and a second convex lens with proper focal lengths are placed, so that the target optical signal light is changed into parallel light, the parallel light enters a third convex lens, a pinhole with a preset size is placed at the rear focal point of the third convex lens, the pinhole is used for filtering the target optical signal and modulating the size of a light spot, a fourth convex lens is placed behind the pinhole, the distance between the pinhole and the fourth convex lens is 2 times of the focal length of the fourth convex lens, an image formed by the pinhole by the fourth convex lens is 2 times of the focal length of the fourth convex lens, a mechanical chopper blade is placed at the position of the 2 times of the focal length of the fourth convex lens, so that the target optical signal is changed into an alternating current signal, a fifth convex lens is placed behind the mechanical chopper blade, the distance between the mechanical chopper blade and the fifth convex lens is the focal length of the fifth convex lens, and finally the target optical signal is enabled to pass through a fourth single mode optical fiber to be coupled into a collimating lens.
As a preferred embodiment, the method further comprises:
and utilizing the narrow linewidth laser local oscillation signal output by the DFB laser with the adjustable center wavelength.
In a second aspect, the invention provides a passive laser heterodyne double balanced spectrum detection device, comprising an optical structure and a radio frequency signal processing structure, wherein,
The optical structure comprises a target optical signal, a first convex lens, a first concave lens, a second convex lens, a third convex lens, a pinhole, a fourth convex lens, a mechanical chopper blade, a fifth convex lens and a collimating lens, wherein the target optical signal is converged at the rear focal point of the first convex lens through the first convex lens, the first concave lens and the second convex lens with proper focal lengths are placed, so that the target optical signal light is changed into parallel light, the parallel light enters the third convex lens, a pinhole with preset size is placed at the rear focal point of the third convex lens, the pinhole is utilized to filter the target optical signal and modulate the size of a light spot, the fourth convex lens is placed behind the pinhole, the distance between the pinhole and the fourth convex lens is 2 times of the focal length of the fourth convex lens, an image formed by the pinhole is 2 times of the focal length of the fourth convex lens behind the fourth convex lens, the mechanical chopper blade is placed at the position of 2 times of the focal length of the fourth convex lens, so that the target optical signal is changed into an alternating current signal, the distance between the pinhole and the fifth convex lens is changed into a single mode through the mechanical chopper blade, and the fifth optical signal is changed into a parallel signal after passing through the fifth convex lens, and finally the mechanical chopper lens is placed;
the radio frequency signal processing structure comprises:
Collecting a target optical signal by using an optical system, wherein the target optical signal is broad-spectrum incoherent light and consists of optical signals with different frequencies, and the complex amplitudes of the optical signals with different frequencies are random functions related to time;
The method comprises the steps of carrying out chopper modulation on a target optical signal by utilizing a chopper, inputting the modulated target optical signal to a target signal input end of an optical mixer, inputting a narrow linewidth laser local oscillation signal to a local oscillation input end of the optical mixer, wherein in the optical mixer, the target optical signal and the narrow linewidth laser local oscillation signal are overlapped, the overlapped target optical signal comprises a direct current part and an alternating current part, wherein a part with the frequency magnitude exceeding the record limit of a photoelectric detector is the direct current part, coherent overlapping is carried out according to the part, close to the frequency of the narrow linewidth laser local oscillation signal, in the target optical signal, of the components, which are detected by the photoelectric detector are called alternating current signals, the optical mixer outputs four paths of photocurrent signals, each path of signals comprises a direct current part and an alternating current part, wherein the direct current part is proportional to the light intensity sum of the narrow linewidth laser signal and the target optical signal, and the relative local oscillation phase difference exists between the alternating current parts, and the relative local oscillation phase difference is 0 respectively 、90、180And 270;
Selecting a proper filtering range to carry out band-pass filtering on four paths of output, inputting two paths of signals of 0 degree and 180 degrees into a pair of photodiodes, carrying out differential processing on the output of the photodiodes, enabling the output electric signals to be called in-phase signals, inputting two paths of signals of 90 degrees and 270 degrees into another pair of photodiodes, and outputting two paths of signals of 90 degrees and 270 degrees into quadrature signals, wherein the in-phase signals and the quadrature signals are twice of an alternating current part of the input signals, and do not contain a direct current part, and the in-phase signals and the quadrature signals have 90-degree phase delay;
And carrying out harmonic detection on the in-phase signal and the quadrature signal through a phase-locked amplifier, wherein a reference signal of the phase-locked amplifier is from the frequency of a chopper, inputting the two paths of signals into an oscilloscope for sampling, squaring and summing the amplitudes of the two paths of signals acquired by the oscilloscope, obtaining a result proportional to the target optical signal intensity at the current moment, obtaining the target optical signal intensity in a preset time, obtaining a calculated average value of the target optical signal intensity in the preset time, and obtaining the light intensity information with high spectral resolution.
Compared with the prior art, the invention has the following beneficial effects:
The method and the device provided by the embodiment of the invention use the optical mixer and the photodiode to carry out mixing and differential processing on the input narrow-linewidth laser local oscillation signal and the wide-spectrum incoherent target optical signal to generate two paths of random time beat frequency optical current signals with 90 degrees of phase difference, the random time beat frequency optical current signals contain information such as the spectrum of signal light, and the like, and the output optical current signals are processed by filtering, integrating and the like to recover the spectral information of the signal light. In addition, the balanced coherent detection is combined with subsequent signal processing steps such as filtering, amplifying and the like, so that the signal quality and the dynamic response range are further improved.
Drawings
FIG. 1 is a schematic flow chart of a passive laser heterodyne double balanced spectrum detection method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of optical field spectral density of the entire photocurrent in a passive heterodyne double balanced spectrum detection method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an optical structure in a passive heterodyne dual balanced spectrum detection method according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a radio frequency signal processing structure in a passive laser heterodyne dual balanced spectrum detection method according to an embodiment of the present invention.
Wherein reference numerals include:
1 is a target optical signal, 2 is a first convex lens, 3 is a first concave lens, 4 is a second convex lens, 5 is a third convex lens, 6 is a pinhole, 7 is a fourth convex lens, 8 is a chopper blade, 9 is a fifth convex lens, 10 is a collimating lens, 11 is a DFB laser, 12 is an optical modulator, 13 is a target signal input end, 14 is a local oscillator input end, and 15 is an optical mixer 90 The mixers, 16 are optical mixers 90The 0 output of the mixer, 17, is an optical mixer 90The 90 output of the mixer, 18 is an optical mixer 90The 180 output of the mixer, 19 is an optical mixer 90The 270 ° outputs of the mixer, 110 are photodiodes, 111 are in-phase signal outputs, 112 are quadrature signal outputs, 113 are bandpass filters, 114 are lock-in amplifiers, 115 are chopper frequencies, 116 are oscilloscopes.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, like modules are denoted by like reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, a detailed description thereof will not be repeated.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limiting the invention.
Referring to fig. 1, the embodiment of the invention provides a passive laser heterodyne double-balanced spectrum detection method, which includes:
s101, collecting a target optical signal by using an optical system, wherein the target optical signal is broad-spectrum incoherent light and consists of optical signals with different frequencies, and the complex amplitudes of the optical signals with different frequencies are random functions related to time.
S102, performing chopper modulation on the target optical signal by using a chopper, inputting the modulated target optical signal to a target signal input end of an optical mixer, inputting a narrow linewidth laser local oscillation signal to a local oscillation input end of the optical mixer, wherein in the optical mixer, the target optical signal and the narrow linewidth laser local oscillation signal are overlapped, the overlapped target optical signal comprises a direct current part and an alternating current part, wherein a part with a frequency magnitude exceeding the record limit of a photoelectric detector is the direct current part, coherent overlapping is performed according to the part, close to the frequency of the narrow linewidth laser local oscillation signal, in the target optical signal, the part detected by the photoelectric detector is called an alternating current signal, the optical mixer outputs four paths of photocurrent signals, each path of local oscillation signal comprises the direct current part and the alternating current part, the direct current part is proportional to the sum of the light intensity of the narrow linewidth laser signal and the target optical signal, and the relative phase difference exists between the alternating current parts and is 0 respectively、90、180And 270。
S103, selecting a proper filtering range to carry out band-pass filtering on four paths of output, inputting two paths of signals of 0 degree and 180 degrees into a pair of photodiodes, carrying out differential processing on the output of the photodiodes, inputting the output electric signals of 90 degrees and 270 degrees into the other pair of photodiodes, and outputting two paths of signals of 90 degrees and 270 degrees into quadrature signals, wherein the in-phase signals and the quadrature signals are twice of an alternating current part of the input signals, and do not contain a direct current part, and the in-phase signals and the quadrature signals have 90-degree phase delay.
And S104, carrying out harmonic detection on the in-phase signal and the quadrature signal through a phase-locked amplifier, wherein a reference signal of the phase-locked amplifier is from the frequency of a chopper, inputting the two paths of signals into an oscilloscope for sampling, squaring and summing the amplitudes of the two paths of signals acquired by the oscilloscope, obtaining a result proportional to the target optical signal intensity at the current moment, obtaining the target optical signal intensity in a preset time, obtaining a calculated average value of the target optical signal intensity in the preset time, and obtaining the light intensity information with high spectral resolution.
In some embodiments, S101 is configured to collect, by using an optical system, a target optical signal, where the target optical signal is a broad spectrum incoherent light, and is composed of light with different frequencies, and complex amplitudes of the light signals with different frequencies are random functions related to time, and the collecting process specifically includes:
The method comprises the steps that a target optical signal is converged at a rear focal point of a first convex lens through the first convex lens, a first concave lens and a second convex lens with proper focal lengths are placed, so that the target optical signal light is changed into parallel light, the parallel light enters a third convex lens, a pinhole with a preset size is placed at the rear focal point of the third convex lens, the pinhole is used for filtering the target optical signal and modulating the size of a light spot, a fourth convex lens is placed behind the pinhole, the distance between the pinhole and the fourth convex lens is 2 times of the focal length of the fourth convex lens, an image formed by the pinhole by the fourth convex lens is 2 times of the focal length of the fourth convex lens, a mechanical chopper blade is placed at the position of the 2 times of the focal length of the fourth convex lens, so that the target optical signal is changed into an alternating current signal, a fifth convex lens is placed behind the mechanical chopper blade, the distance between the mechanical chopper blade and the fifth convex lens is the focal length of the fifth convex lens, and finally the target optical signal is enabled to pass through a fourth single mode optical fiber to be coupled into a collimating lens.
In some embodiments, a narrow linewidth laser local oscillator signal is output using a DFB laser with a tunable center wavelength.
In S102, the chopper is used to chop and modulate the target optical signal, the modulated target optical signal is input to the target signal input end of the optical mixer, the narrow linewidth laser local oscillation optical signal is input to the local oscillation input end of the optical mixer, in the optical mixer, the target optical signal and the narrow linewidth laser local oscillation optical signal are superimposed, the superimposed optical signal includes two parts, wherein the part with the frequency magnitude exceeding the record limit of the photodetector is a direct current part, and the direct current part can be regarded as a constant and does not change with time. According to the coherent superposition of the components in the target optical signal, which are close to the frequency of the narrow linewidth laser local oscillation optical signal, the magnitude of the frequency is reduced toThe part that can be detected by the photodetector is called an ac part, which can be regarded as random beat information. The optical mixer outputs four paths of photocurrent signals, each path of signal comprises a direct current part and an alternating current part, wherein the direct current parts are in direct proportion to the sum of the light intensities of the local oscillation optical signal and the target optical signal, and relative phase differences exist between the alternating current parts and are respectively 0、90、180And 270。
In S103, the four paths of output signals are bandpass filtered, and an appropriate filtering range is selected, so that the influence of noise of local oscillation light itself, environmental noise and the like on the signals is reduced. Two paths of signals of 0 degree and 180 degrees are input into a pair of photodiodes, the outputs of the photodiodes are subjected to differential processing, the output electric signals are called in-phase signals, two paths of signals of 90 degrees and 270 degrees are input into the other pair of photodiodes, the outputs of the two paths of signals of 90 degrees and 270 degrees are quadrature signals, the in-phase signals and the quadrature signals are twice of alternating current parts of the input signals, the direct current parts are not included, and the in-phase signals and the quadrature signals have phase delays of 90 degrees.
In S104, harmonic detection is performed on the in-phase signal and the quadrature signal through a lock-in amplifier, where a reference signal of the lock-in amplifier is derived from a frequency of a chopper, the two signals are input to an oscilloscope for sampling, a square sum is performed according to an amplitude of the two signals collected by the oscilloscope, and an obtained result is in direct proportion to a signal intensity of the target light at a current moment. The signal intensity in a period of time is obtained, the calculated average value in the period of time is obtained and can be regarded as the target light intensity in the band-pass filtering range, and the light intensity information with high spectral resolution can be obtained by changing the filtering range and the local oscillation frequency.
According to the passive laser heterodyne double-balance spectrum detection method provided by the embodiment of the invention, the coherent superposition of partial target light with the frequency close to that of the local oscillator light and the local oscillator light is realized by selecting the proper local oscillator light and coupling the proper local oscillator light with the target light reflected or emitted by the target, so that the passive spectrum subdivision is realized, and the output difference frequency signal is completely consistent with the spectrum distribution of the target signal.
Because the target signal is a broad-spectrum incoherent light, the signal light is considered to be a random wave, namely, a polarization unit vector and a complex amplitude are random functions related to time and position, the target light is collected through an optical system, local oscillation light is generated inside the device, two beams of light are overlapped on the surface of a photoelectric detector, the intensity of a synthesized light field is in direct proportion to the mode size of the two beams of light after being overlapped, and photocurrent is formed on the surface of the detector. The photocurrent comprises a direct current component and an alternating current component, the direct current component is in direct proportion to the sum of the light intensities of the two beams of light, is irrelevant to time, can be regarded as background noise, and the alternating current component is related to the light field formed by overlapping the signal light and the local oscillation light and changes along with the angular frequency difference of the two beams of light. The alternating current signal contains information of the intensity, the frequency difference and the phase difference of the target light and the local oscillation light. When the local oscillation light information is known, the information such as the intensity, the frequency and the phase of the target light can be deduced through alternating current components. The direct current signal can be regarded as the sum of the light intensity of the target light and the local oscillation light, and the information such as the phase, the frequency and the like of the modulation signal does not change the amplitude of the generated photocurrent, so that the direct current signal is inhibited or filtered when heterodyne detection is carried out.
Typically, the polarization state and complex amplitude of natural light are statistically independent functions. Thus, the average of their products can be broken down into independent averages of the polarisation and amplitude random functions. And the phase of the signal field is atSince the interval (c) may exist, if the time average value is directly obtained for the photocurrent, the ac part is 0. But this does not represent an ac portion of the heterodyne detection output with an amplitude of 0. To understand this, the following assumptions are first made, 1. All random variables of the received light are considered to be stationary in time. 2. The polarization of the reference wave can be considered independent of spatial coordinates and time. 3. The intensity of the reference wave is always much greater than the intensity of the signal wave. 4. The signal wave and the reference wave are assumed to be spatially coherent within the sensitive area of the photodetector. Since the ac part is related to the frequency difference and the fourier transform of the spectral density is a correlation function, the photocurrent is calculated first at two different times,Is a function of the correlation function of (a). The correlation function of the photocurrent comprises a correlation function of background noise, a correlation function of local oscillator light intensity, a correlation function of a coherent superposition amplitude coefficient and a correlation function of target field complex amplitude. The coherent superimposed light intensity coefficient refers to the ratio of the projection of the target light in the polarization direction of the local oscillation light to the self-amplitude of the target light at a certain moment, and can be understood as the cosine of the included angle between the polarization direction of the target signal and the polarization direction of the local oscillation light. Then Fourier transform is carried out on the correlation function of the photoelectric current to obtain the frequency spectrum density of the photoelectric current, including the frequency spectrum density of the noise part and the local oscillator light intensitySpectral density of output difference frequency signal. Wherein the method comprises the steps ofIs the spectral density of the coherent superimposed amplitude coefficients,、The spectral densities of the target light and local oscillator light amplitudes, respectively.And (3) withPhysically meaning the spectral density of the projection of the signal complex amplitude vector in the direction of local oscillator light vector. If the local oscillation light is monochromatic wave, the spectral density of the local oscillation light can be considered as a delta function, and the spectrum of the output difference frequency signal can be considered to be completely consistent with the spectral distribution of the target. The optical field spectral density of the photocurrent as a whole is shown in fig. 2.
With reference to fig. 3, the passive laser heterodyne double-balanced spectrum detection method provided by the invention correspondingly comprises an optical structure and a radio frequency signal processing structure. The optical structure mainly comprises that a target optical signal 1 is converged at the rear focal point of a first convex lens 2 through the first convex lens 2, then a first concave lens 3 and a second convex lens 4 with proper focal lengths are placed, signal light is changed into parallel light, the parallel light enters a third convex lens 5, a pinhole 6 with proper size is placed at the rear focal point of the third convex lens 5, the target optical signal 1 is filtered and modulated by the pinhole 6, a fourth convex lens 7 is placed behind the pinhole 6, the distance between the pinhole 6 and the fourth convex lens 7 is 2 times of the focal length of the fourth convex lens 7, an image formed by the pinhole 6 by the fourth convex lens 7 is 2 times of the focal length behind the fourth convex lens 7, a mechanical chopper blade 8 is placed at the 2 times of the focal length behind the fourth convex lens 7, the target optical signal 1 is changed into an alternating current signal, a fifth convex lens 9 is placed behind the chopper blade 8, and the distance between the chopper blade 8 and the fifth convex lens 9 is the focal length of the fifth convex lens 9. Finally, the target optical signal 1 is changed into parallel light after passing through the fourth convex lens 9, the parallel light is coupled into a single mode fiber through the collimating lens 10, and the target optical signal is transmitted to the radio frequency signal processing structure through the single mode fiber.
The target optical signal 1 is characterized by a broad spectrum of incoherent light, which may be sunlight, halogen lamps or spontaneous emissions of objects, etc. The first concave lens 3 and the second convex lens 4 are used for adjusting the signal light to parallel light, so that the subsequent light path adjustment is facilitated, and the size of the pinhole 6 is matched with the blade width of the mechanical chopper blade 8, so that the modulation frequency and extinction ratio of the signal light meet the requirements.
The radio frequency signal processing structure mainly includes that a target optical signal collected by an optical structure is firstly connected into an optical modulator 12, the optical modulator 12 can adopt a semiconductor amplifier, the optical modulator 12 amplifies the target optical signal, then the amplified target optical signal is input into a target signal input end 13 of an optical mixer 15, in addition, a narrow line width laser local oscillation signal output by a DFB laser 1 with adjustable center wavelength is input into a local oscillation input end 14 of the optical mixer 15, and the optical mixer 15 can adopt a 90-degree optical mixer. The optical mixer 15 performs coherent superposition of local oscillation light and signal light to output four signals, each signal includes a direct current part and an alternating current part, wherein the direct current part is proportional to the sum of the light intensities of the local oscillation light and the signal light, a relative phase difference exists between the alternating current parts, and 16 is the optical mixer 90The 0 output of the mixer, 17, is an optical mixer 90The 90 output of the mixer, 18 is an optical mixer 90The 180 output of the mixer, 19 is an optical mixer 90270 ° Output of mixer, wherein optical mixer 900 Output 16 of the mixer and optical mixer 90180 Deg. output 180 of mixerThe 18 output port branch is called in-phase branch I-arm, optical mixer 9090 DEG output 17 of a mixer and an optical mixer 90The 270 output 19 output port branch of the mixer is called the quadrature branch Q-arm.
Signals of the same-direction branch and the orthogonal branch are respectively input into the photodiodes 110, and the two photodiodes 110 form a detection unit, and the outputs of the two detection units are respectively called an in-phase signal 111 and an orthogonal signal 112. The two paths of output signals eliminate the direct current part of the input signal, and the alternating current part is doubled to the input signal.
The two signals are input into a band-pass filter 113 with the same parameters, the signals are subjected to band-pass filtering, harmonic detection is carried out on the two signals through a phase-locked amplifier 114, wherein a reference signal of the phase-locked amplifier 114 is from a frequency 115 of a chopper, and finally the two signals are input into an oscilloscope 116 for sampling. The sum of squares is based on the amplitude of the two signals collected by the oscilloscope 116, which yields a result proportional to the intensity of the target light.
As an embodiment, the passive laser heterodyne double-balance spectrum detection method provided by the embodiment of the invention specifically uses a 90-degree mixer and four photodiodes to carry out mixing and differential processing on an input narrow-linewidth laser local oscillation signal and a wide-spectrum incoherent target optical signal to generate two paths of random time beat frequency optical current signals with 90-degree phase difference, the random time beat frequency optical current signals contain information such as the spectrum of signal light, the output optical current signals are processed by filtering, integrating and other methods to recover the spectrum information of the signal light, by using the method, the narrow linewidth and wavelength tunable characteristic of the narrow linewidth laser local oscillation signal can be utilized to acquire high spectral resolution information of the wide spectrum incoherent optical signal, the utilization efficiency of local oscillation light is effectively improved, common mode noise and partial system noise are eliminated, the signal to noise ratio of an output signal is enhanced, the system can still keep higher detection precision and stability under the condition that the stability of the local oscillation light fluctuates, and the requirement on the stability of the local oscillation light is remarkably reduced. In addition, the balanced coherent detection is combined with subsequent signal processing steps such as filtering, amplifying and the like, so that the signal quality and the dynamic response range are further improved.
Correspondingly, the embodiment of the invention provides a passive laser heterodyne double-balance spectrum detection device, which comprises an optical structure and a radio frequency signal processing structure, wherein,
The optical structure comprises a target optical signal, a first convex lens, a first concave lens, a second convex lens, a third convex lens, a pinhole, a fourth convex lens, a mechanical chopper blade, a fifth convex lens and a collimating lens, wherein the target optical signal is converged at the rear focal point of the first convex lens through the first convex lens, the first concave lens and the second convex lens with proper focal lengths are placed, so that the target optical signal light is changed into parallel light, the parallel light enters the third convex lens, a pinhole with preset size is placed at the rear focal point of the third convex lens, the pinhole is utilized to filter the target optical signal and modulate the size of a light spot, the fourth convex lens is placed behind the pinhole, the distance between the pinhole and the fourth convex lens is 2 times of the focal length of the fourth convex lens, an image formed by the pinhole is 2 times of the focal length of the fourth convex lens behind the fourth convex lens, the mechanical chopper blade is placed at the position of 2 times of the focal length of the fourth convex lens, so that the target optical signal is changed into an alternating current signal, the distance between the pinhole and the fifth convex lens is changed into a single mode through the mechanical chopper blade, and the fifth optical signal is changed into a parallel signal after passing through the fifth convex lens, and finally the mechanical chopper lens is placed;
the radio frequency signal processing structure comprises:
The method comprises the steps of carrying out chopper modulation on a target optical signal by utilizing a chopper, inputting the modulated target optical signal to a target signal input end of an optical mixer, inputting a narrow linewidth laser local oscillation signal to a local oscillation input end of the optical mixer, wherein in the optical mixer, the target optical signal and the narrow linewidth laser local oscillation signal are overlapped, the overlapped target optical signal comprises a direct current part and an alternating current part, wherein a part with the frequency magnitude exceeding the record limit of a photoelectric detector is the direct current part, coherent overlapping is carried out according to the part, close to the frequency of the narrow linewidth laser local oscillation signal, in the target optical signal, of the components, which are detected by the photoelectric detector are called alternating current signals, the optical mixer outputs four paths of photocurrent signals, each path of signals comprises a direct current part and an alternating current part, wherein the direct current part is proportional to the light intensity sum of the narrow linewidth laser signal and the target optical signal, and the relative local oscillation phase difference exists between the alternating current parts, and the relative local oscillation phase difference is 0 respectively 、90、180And 270;
Selecting a proper filtering range to carry out band-pass filtering on four paths of output, inputting two paths of signals of 0 degree and 180 degrees into a pair of photodiodes, carrying out differential processing on the output of the photodiodes, enabling the output electric signals to be called in-phase signals, inputting two paths of signals of 90 degrees and 270 degrees into another pair of photodiodes, and outputting two paths of signals of 90 degrees and 270 degrees into quadrature signals, wherein the in-phase signals and the quadrature signals are twice of an alternating current part of the input signals, and do not contain a direct current part, and the in-phase signals and the quadrature signals have 90-degree phase delay;
And carrying out harmonic detection on the in-phase signal and the quadrature signal through a phase-locked amplifier, wherein a reference signal of the phase-locked amplifier is from the frequency of a chopper, inputting the two paths of signals into an oscilloscope for sampling, squaring and summing the amplitudes of the two paths of signals acquired by the oscilloscope, obtaining a result proportional to the target optical signal intensity at the current moment, obtaining the target optical signal intensity in a preset time, obtaining a calculated average value of the target optical signal intensity in the preset time, and obtaining the light intensity information with high spectral resolution.
The passive laser heterodyne double-balanced spectrum detection device provided by the embodiment of the invention uses the optical mixer and the photodiode to carry out mixing and differential processing on the input narrow-linewidth laser local oscillation signal and the wide-spectrum incoherent target optical signal to generate two paths of random time beat frequency photoelectric signals with 90 degrees of phase difference, the random time beat frequency photoelectric signals contain information such as the spectrum of signal light, and the like, and the output photoelectric signals can be processed by filtering, integrating and the like to recover the spectrum information of the signal light. In addition, the balanced coherent detection is combined with subsequent signal processing steps such as filtering, amplifying and the like, so that the signal quality and the dynamic response range are further improved.
While embodiments of the present invention have been illustrated and described above, it will be appreciated that the above described embodiments are illustrative and should not be construed as limiting the invention. Variations, modifications, alternatives and variations of the above-described embodiments may be made by those of ordinary skill in the art within the scope of the present invention.
The above embodiments of the present invention do not limit the scope of the present invention. Any other corresponding changes and modifications made in accordance with the technical idea of the present invention shall be included in the scope of the claims of the present invention.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202411787051.3A CN119245829B (en) | 2024-12-06 | 2024-12-06 | A passive laser heterodyne double-balanced spectrum detection method and device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202411787051.3A CN119245829B (en) | 2024-12-06 | 2024-12-06 | A passive laser heterodyne double-balanced spectrum detection method and device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN119245829A true CN119245829A (en) | 2025-01-03 |
| CN119245829B CN119245829B (en) | 2025-03-21 |
Family
ID=94030441
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202411787051.3A Active CN119245829B (en) | 2024-12-06 | 2024-12-06 | A passive laser heterodyne double-balanced spectrum detection method and device |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN119245829B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN120049965A (en) * | 2025-04-15 | 2025-05-27 | 中国科学院长春光学精密机械与物理研究所 | Optical signal passive differential frequency detection and digital coherent superposition device and method |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111141493A (en) * | 2019-12-27 | 2020-05-12 | 中国科学院合肥物质科学研究院 | Instrumental Line Function Measurement Method of Laser Heterodyne Spectrometer |
| CN114184568A (en) * | 2021-11-04 | 2022-03-15 | 合肥学院 | All-fiber mid-infrared laser heterodyne radiometer system |
| US20240035889A1 (en) * | 2022-07-27 | 2024-02-01 | Seiko Epson Corporation | Optical Device And Spectroscopy Apparatus |
| CN117572443A (en) * | 2023-10-31 | 2024-02-20 | 哈尔滨工业大学 | A fast and high-precision nonlinear correction system and method for swept frequency interferometry based on non-uniform zero interpolation filtering |
| CN118999791A (en) * | 2024-08-15 | 2024-11-22 | 中国科学院长春光学精密机械与物理研究所 | Super spectrum detection method based on heterodyne technology and online super spectrum detector adopting same |
-
2024
- 2024-12-06 CN CN202411787051.3A patent/CN119245829B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111141493A (en) * | 2019-12-27 | 2020-05-12 | 中国科学院合肥物质科学研究院 | Instrumental Line Function Measurement Method of Laser Heterodyne Spectrometer |
| CN114184568A (en) * | 2021-11-04 | 2022-03-15 | 合肥学院 | All-fiber mid-infrared laser heterodyne radiometer system |
| US20240035889A1 (en) * | 2022-07-27 | 2024-02-01 | Seiko Epson Corporation | Optical Device And Spectroscopy Apparatus |
| CN117572443A (en) * | 2023-10-31 | 2024-02-20 | 哈尔滨工业大学 | A fast and high-precision nonlinear correction system and method for swept frequency interferometry based on non-uniform zero interpolation filtering |
| CN118999791A (en) * | 2024-08-15 | 2024-11-22 | 中国科学院长春光学精密机械与物理研究所 | Super spectrum detection method based on heterodyne technology and online super spectrum detector adopting same |
Non-Patent Citations (1)
| Title |
|---|
| 惠玉泽: "《中国优秀硕士学位论文全文数据库 信息科技辑》", 15 March 2024, pages: 13 - 15 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN120049965A (en) * | 2025-04-15 | 2025-05-27 | 中国科学院长春光学精密机械与物理研究所 | Optical signal passive differential frequency detection and digital coherent superposition device and method |
| CN120049965B (en) * | 2025-04-15 | 2025-07-01 | 中国科学院长春光学精密机械与物理研究所 | Optical signal passive differential frequency detection and digital coherent superposition device and method |
Also Published As
| Publication number | Publication date |
|---|---|
| CN119245829B (en) | 2025-03-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US8699029B2 (en) | Miniaturized laser heterodyne radiometer for carbon dioxide, methane and carbon monoxide measurements in the atmospheric column | |
| CN119245829B (en) | A passive laser heterodyne double-balanced spectrum detection method and device | |
| CN108332735B (en) | Resonance type fiber-optic gyroscope coherent demodulation system and method based on external beam interference | |
| KR101603909B1 (en) | Photomixing-based CW Terahertz Generation and Detection Apparatus Utilizing the Phase Noise Compensation Method | |
| US10215845B2 (en) | Simultaneous ranging and remote chemical sensing utilizing optical dispersion or absorption spectroscopy | |
| CN106680831B (en) | Laser Active Coherent Balance Detection Polarization Analyzer | |
| CN111781153A (en) | A wavelength-modulated active laser heterodyne spectroscopy gas telemetry method | |
| US7417744B2 (en) | Coherent hybrid electromagnetic field imaging | |
| US7978341B2 (en) | Multi-channel laser interferometric method and apparatus for detection of ultrasonic motion from a surface | |
| EP1253730A2 (en) | Method and system for optical spectrum analysis with matched filter detection | |
| CN118549383B (en) | A trace gas concentration detection device based on heterodyne phase-sensitive dispersion | |
| US7265849B2 (en) | Systems and methods for determining the spectral content of an optical signal | |
| US20170048001A1 (en) | Apparatus and Method for Isolating an Optical Signal by Subtracting the Atmospheric Background in Real Time | |
| CN101126775B (en) | Broad band and high resolution ratio millimeter wave and sub millimeter wave signal detecting system | |
| US7068374B2 (en) | Phase-diverse coherent optical spectrum analyzer | |
| JP2005172832A (en) | Spectral phase measurement using coherent optical spectrum analyzer with various phases | |
| CN118549384B (en) | An airborne atmospheric methane leak remote sensing device | |
| CN120213226B (en) | An equivalent wavelength phase stabilization system for Fourier ultrafast spectroscopy | |
| CN110376600A (en) | One kind being based on the modified moving target motion feature measurement method of Doppler frequency spectrum | |
| CN110133678A (en) | A method for improving the measurement range of a phase-modulated laser Doppler velocimetry system | |
| CN216132474U (en) | A fiber grating center wavelength demodulation system and demodulator | |
| EP1669729A1 (en) | A phase-diverse coherent optical spectrum analyzer | |
| Loukisa et al. | Analysis of Photonics-Enabled FMCW THz Spectrometers for Non-Destructive Thickness Measurements | |
| d'Auria et al. | Image formation using antenna properties of optical heterodyne receivers | |
| JPH06273386A (en) | Ultrasonic detector |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |