A phase compensation based resonant dual-comb opto-acoustic spectroscopy system and method

Abstract

The application discloses a resonant dual-comb photoacoustic spectrum system and method based on phase compensation, comprising a dual-comb source, a beam splitter, a gas chamber, a resonant acoustic-electric transducer, a preamplifier, a photoelectric detector, a quadrature detector, a dual-channel function generator, a phase shifter and a phase-locked amplifier; the phase fluctuation information of each comb tooth pair after down-conversion is extracted by the quadrature detector, and the phase fluctuation information is applied to the two channels of the dual-channel phase-locked amplifier by the phase shifter, so as to be used as the reference input signal of the phase-locked amplifier. On this basis, the phase locking of the photoacoustic signal and the reference input signal is realized, so that the influence of the phase fluctuation noise on the phase-sensitive demodulation process is suppressed, and the signal-to-noise ratio of the system is improved. The technical scheme can effectively solve the problem of sensitivity reduction of the resonant dual-comb photoacoustic spectrum system caused by phase fluctuation.

Description

Technical Field

[0001] This invention relates to the field of dual-comb photoacoustic spectroscopy technology, and in particular to a resonant dual-comb photoacoustic spectroscopy system and method based on phase compensation. Background Technology

[0002] Photoacoustic spectroscopy, due to its advantages such as high sensitivity, lack of wavelength selectivity, and large dynamic range, has been widely used in trace gas detection fields, such as air pollution monitoring, factory emission monitoring, and medical disease diagnosis. Dual-comb photoacoustic spectroscopy uses a dual-comb source as the excitation source, combining the advantages of both photoacoustic and dual-comb spectroscopy to achieve wide spectral range, high sensitivity, high resolution, short time, and large dynamic range. Its principle is as follows: two optical frequency combs with slightly different repetition frequencies (i.e., a dual-comb) undergo intensity modulation of a low-frequency envelope due to the beat frequency effect when down-converted to the acoustic frequency domain. After the intensity-modulated dual-comb light source interacts with gas molecules, the gas molecules absorb light energy at the comb tooth frequencies due to the photoacoustic effect, generating a multiheterodyne acoustic signal. The frequency components of the generated multiheterodyne acoustic signal are consistent with the down-conversion frequencies of each comb tooth pair in the dual-comb. The multiheterodyne acoustic signal is detected by a resonant acoustic-electric transducer and converted into an electrical signal output. Resonant dual-comb photoacoustic spectroscopy employs resonant acousto-electric devices as resonant acousto-electric transducers, enabling the detection of resonant components in multi-heterodyne acoustic signals and improving the system's signal-to-noise ratio. It is of great significance for achieving broadband high-sensitivity spectroscopy, high-resolution molecular spectroscopy, and multi-gas detection.

[0003] However, in practical applications, slight differences exist between the two optical frequency combs that make up the dual optical comb along their optical paths, such as due to temperature and stress. This phenomenon is particularly pronounced in near-infrared fiber-based dual optical comb sources. This imperfect symmetry in the optical path causes a phase shift in the low-frequency envelope of each comb tooth pair after the two optical frequency combs are combined, resulting in a phase shift in the photoacoustic signal at the corresponding frequency of each comb tooth pair. In traditional dual optical comb photoacoustic spectroscopy, this effect can only be suppressed by extracting the low-frequency drift component. However, for resonant dual optical comb photoacoustic spectroscopy, suppressing the phase shift at specific frequencies after down-conversion of the comb tooth pairs is often more meaningful because the lock-in amplifier used in the demodulation process of resonant dual optical comb photoacoustic spectroscopy needs to ensure phase locking between the signal and the reference. Such phase shift has a significant impact on the lock-in amplifier demodulation process, affecting the system's signal-to-noise ratio. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, a resonant dual-comb photoacoustic spectroscopy system and method based on phase compensation is provided. This method extracts the phase fluctuation of specific frequency components of the background light intensity after down-conversion from a multiheterodyne signal using orthogonal detectors and photodetectors. The reference input of the orthogonal detector is the output of one channel of a dual-channel function generator. The extracted phase fluctuation information is then applied to the output of the second channel of the dual-channel function generator via a phase shifter. The phase-shifted output serves as the reference input of a lock-in amplifier, compensating for the phase. Under these conditions, the signal input and reference input of the lock-in amplifier exhibit consistent phase changes. Therefore, phase locking is achieved through phase compensation, thereby improving the system's signal-to-noise ratio and sensitivity, and enhancing the performance of the resonant dual-comb photoacoustic spectroscopy sensing system.

[0005] To achieve the objectives of this invention, a phase-compensated resonant dual-comb photoacoustic spectroscopy system is provided, comprising a dual-comb source, a beam splitter, a gas cell, a resonant acoustic-electric transducer, a preamplifier, a photodetector, a quadrature detector, a dual-channel function generator, a phase shifter, and a lock-in amplifier. The beam splitter has a splitting ratio of 99:1, where 1% of the light enters the photodetector to extract phase fluctuation information, and 99% of the light enters the gas cell to interact with gas molecules. The dual-comb source is split into two paths by the beam splitter, one of which is connected to the photodetector to receive the background light intensity signal from the dual-comb source. The intensity change information of the dual-comb source is converted into [the signal] through the photoelectric effect. An electrical signal is output, and the output electrical signal is passed through an orthogonal detector to extract the phase fluctuation value at a specific frequency after downconversion, and applied to a phase shifter. The reference signal of the orthogonal detector is provided by one channel of a dual-channel function generator, and the second channel of the dual-channel function generator is sent to the phase shifter. After phase shifting, the phase shifter outputs the signal as the reference signal of the lock-in amplifier. The other path of the dual optical comb source enters the gas chamber and interacts with the gas molecules in the gas chamber to generate a photoacoustic effect. The sound wave generated by the photoacoustic effect is converted into an electrical signal by a resonant acoustic-electric transducer. The preamplifier amplifies the electrical signal and sends it to the lock-in amplifier for demodulation to obtain the dual optical comb photoacoustic spectrum signal.

[0006] As a further improvement to the above scheme, the dual optical comb source consists of two optical frequency combs with a slight difference in repetition frequency, generated by electro-optic modulation of a continuous wave laser in the communication band, and the input and output of each device are integrated by optical fiber.

[0007] As a further improvement to the above scheme, the phase shifter has two input terminals. One input terminal is connected to the second channel of the dual-channel function generator, and the other input terminal is used to load the phase fluctuation extracted by the quadrature detector onto the output of the second channel of the dual-channel function generator, serving as the reference input terminal of the lock-in amplifier.

[0008] As a further improvement to the above scheme, the dual-channel function generator outputs signals with the same frequency and phase from both channels, with the output frequency being the resonant frequency and the output phase being set to zero.

[0009] A method for a phase-compensated resonant dual-comb photoacoustic spectroscopy system includes the following steps:

[0010] Step 1: Fill the gas chamber with the gas sample to be tested;

[0011] Step 2: The dual optical comb source is split into two paths. One path enters the photodetector, which converts the light intensity change signal into an electrical signal. The other path enters the gas chamber, where it interacts with gas molecules to generate an acoustic signal. This acoustic signal is generated due to the photoacoustic effect.

[0012] Step 3: One channel of the dual-channel function generator provides a reference signal to the quadrature detector. The quadrature detector extracts the phase fluctuation signal from the electrical signal output by the photodetector and applies this phase fluctuation signal to the output of the second channel of the dual-channel function generator through a phase shifter to provide a reference signal to the lock-in amplifier. The phase fluctuation is mainly caused by the asymmetry of the optical paths of the two optical frequency combs that make up the dual optical comb source due to temperature, strain, etc., which causes phase drift in the low-frequency envelope of each comb tooth pair when the frequency is beat after beam combining.

[0013] Step 4: The acoustic signal is converted into an electrical signal by a resonant acoustic-electric transducer and amplified by a preamplifier. The amplified signal is then sent to a lock-in amplifier for demodulation. Since this signal has the same phase change as the reference signal, the phase-compressed dual-comb photoacoustic spectral signal is obtained. Therefore, phase compensation is achieved in the demodulation process, improving demodulation accuracy and thus increasing the sensitivity of the resonant dual-comb photoacoustic spectroscopy system.

[0014] The beneficial effects of this invention are:

[0015] Compared with existing technologies, the present invention provides a resonant dual-comb photoacoustic spectroscopy system and method based on adaptive phase compensation. It employs orthogonal detectors to extract phase fluctuations at the downconversion frequency of the dual-comb source teeth, and then applies these phase fluctuations to the reference input of a lock-in amplifier used for demodulating the photoacoustic signal via a phase shifter. This phase compensation achieves phase locking between the dual-comb photoacoustic signal and the reference signal. This method improves the system's signal-to-noise ratio, suppresses demodulation noise caused by phase fluctuations, enhances the system's sensitivity for dual-comb photoacoustic spectroscopy, and advances its application. Attached Figure Description

[0016] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0017] Figure 1 Schematic diagram of a resonant dual-comb photoacoustic spectroscopy device;

[0018] Figure 2 This is a schematic diagram of a phase compensation device. Detailed Implementation

[0019] like Figure 1 As shown in the figure, the present invention provides a resonant dual-comb photoacoustic spectroscopy system based on phase compensation, as illustrated in the schematic diagram. Figure 1 As shown, the system includes a dual optical comb source 1, a beam splitter 2, an air chamber 6, a resonant acoustic-electric transducer 5, a preamplifier 7, a photodetector 3, a quadrature detector 4, a dual-channel function generator 9, a phase shifter 10, and a lock-in amplifier 8. The quadrature detector 4 demodulates the frequency fluctuation component to be extracted using the first harmonic. The phase output of the quadrature detector 4 is the phase fluctuation value at the demodulated frequency. The dual optical comb source 1 is split into two paths by the beam splitter 2. One path is connected to the photodetector 3 to receive the background light intensity signal from the dual optical comb source. The intensity change information of the dual optical comb source 1 is converted into an electrical signal output through the photoelectric effect. The output electrical signal is then processed by the quadrature detector 4 to extract the phase fluctuation value at a specific frequency after conversion and applied to the phase shifter 10. The reference signal of the quadrature detector 4 is provided by one channel of the dual-channel function generator 9. The second channel of the dual-channel function generator 9 is sent to the phase shifter 10. After phase shifting, the signal is output by the phase shifter 10 as the reference signal of the lock-in amplifier 8. The other path of the dual optical comb source 1 enters the gas chamber 6 and interacts with the gas molecules in the gas chamber 6 to generate a photoacoustic effect. The sound wave generated by the photoacoustic effect is converted into an electrical signal by the resonant acoustic transducer 5. A typical resonant acoustic transducer 5 can be a quartz tuning fork. The preamplifier 7 amplifies the electrical signal and sends it to the lock-in amplifier 8 for demodulation to obtain the dual optical comb photoacoustic spectrum signal. After phase compensation, the frequency and phase of the signal input terminal of the lock-in amplifier 8 are consistent with the reference input terminal.

[0020] As a further improvement to the above scheme, the dual-optical comb source 1 consists of two optical frequency combs. Furthermore, due to the requirements of molecular relaxation rate, the down-conversion frequency range of each comb pair in the dual-optical comb source 1 is located within the audio frequency range.

[0021] As a further improvement to the above scheme, the phase shifter 10 has two input terminals. One input terminal is connected to the two channels of the dual-channel function generator 9, and the other input terminal is used to load the phase fluctuation extracted by the quadrature detector 4 onto the output of the two channels of the dual-channel function generator 9, serving as the reference input terminal of the lock-in amplifier 8.

[0022] As a further improvement to the above scheme, the dual-channel function generator 9 outputs signals with the same frequency and phase in both channels, with the output frequency being the resonant frequency and the output phase being set to zero.

[0023] A method for a phase-compensated resonant dual-comb photoacoustic spectroscopy system, the specific implementation process of which is as follows: Figure 2 As shown below, it includes the following steps:

[0024] Step 1: The dual optical comb source 1 is split into two paths. One path enters the photodetector 3, which converts the light intensity change signal into an electrical signal. The other path enters the gas chamber 6, where it interacts with gas molecules to generate an acoustic signal. This acoustic signal is generated due to the photoacoustic effect.

[0025] Step 2: One channel of the dual-channel function generator 9 provides a reference signal to the quadrature detector 4. The quadrature detector 4 extracts the phase fluctuation signal from the electrical signal output by the photodetector 3, and applies the phase fluctuation signal to the output of the second channel of the dual-channel function generator 9 through the phase shifter 10 to provide a reference signal to the lock-in amplifier 8.

[0026] Step 3: The acoustic signal is converted into an electrical signal by the resonant acoustic-electric transducer 5, and amplified by the preamplifier 7. The amplified signal is then sent to the lock-in amplifier 8 for demodulation, resulting in the final phase-compensated dual-comb photoacoustic spectral signal. Since this signal has the same phase change as the reference signal, phase compensation is achieved during the demodulation process, improving demodulation accuracy and thus enhancing the sensitivity of the resonant dual-comb photoacoustic spectroscopy system.

[0027] The working principle of the quadrature detector 4 in this invention is to extract the phase difference of the input signal relative to the reference output terminal through two phase-sensitive demodulations with a 90-degree phase difference, that is, the phase change of each comb tooth relative to the zero phase at the corresponding frequency, which is also the phase change of the photoacoustic signal relative to the zero phase.

[0028] In this invention, due to the phase compensation process, the photoacoustic signal input to the lock-in amplifier 8 has the same phase change as the reference signal (i.e., the two-channel signal of the dual-channel function generator 9 after phase shift).

[0029] In this invention, a resonant acoustic-electric transducer 5 is provided as follows: a quartz tuning fork is used as the resonant acoustic-electric transducer 5, and the narrow response bandwidth and immunity to environmental noise of the quartz tuning fork are utilized to further improve the signal-to-noise ratio of the system.

[0030] In this invention, the beam splitting scheme provided by the dual optical comb source is as follows: 1% enters the photodetector 5, and 99% is collimated into the injection chamber 6.

[0031] The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments can be combined with each other to form new embodiments. The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the technical solutions of the present invention.

Claims

1. A phase-compensated resonant dual-comb photoacoustic spectroscopy system, characterized in that: The system includes a dual optical comb source (1), a beam splitter (2), an air chamber (6), a resonant acoustic-electric transducer (5), a preamplifier (7), a photodetector (3), a quadrature detector (4), a dual-channel function generator (9), a phase shifter (10), and a lock-in amplifier (8). The dual optical comb source (1) is split into two paths by the beam splitter (2), one of which is connected to the photodetector (3). The intensity change information of the dual optical comb source (1) is converted into an electrical signal output through the photoelectric effect. The output electrical signal is processed by the quadrature detector (4) to extract the phase fluctuation value at a specific frequency after conversion and applied to the phase shifter (10). The reference signal of the quadrature detector (4) is given by one channel of the dual-channel function generator (9), and the other two channels of the dual-channel function generator (9) are sent to the phase shifter (10). After phase shifting, the signal is generated by the phase shifter. The output of the phase shifter (10) serves as the reference signal for the lock-in amplifier (8); the other path of the dual optical comb source (1) enters the gas chamber (6) and interacts with the gas molecules in the gas chamber (6) to generate a photoacoustic effect. The sound wave generated by the photoacoustic effect is converted into an electrical signal by the resonant acoustic transducer (5). The preamplifier (7) amplifies the electrical signal and sends it to the lock-in amplifier (8) for demodulation to obtain the dual optical comb photoacoustic spectrum signal. The dual optical comb source (1) consists of two optical frequency combs with a small difference in repetition frequency. The phase shifter (10) has two input terminals. One input terminal is connected to the two channels of the dual-channel function generator (9), and the other input terminal is used to load the phase fluctuation extracted by the quadrature detector (4) onto the output of the two channels of the dual-channel function generator (9) as the reference input terminal of the lock-in amplifier (8).

2. The resonant dual-comb photoacoustic spectroscopy system based on phase compensation according to claim 1, characterized in that: The dual-channel function generator (9) outputs signals with the same frequency and phase in both channels.

3. A method for using the phase-compensated resonant dual-comb photoacoustic spectroscopy system as described in claim 2, characterized in that: The steps include the following: Step 1: Fill the gas sample to be tested into the gas chamber (6); Step 2: The dual optical comb source (1) is split into two paths. One path enters the photodetector (3) to convert the light intensity change signal into an electrical signal; the other path enters the gas chamber (6) to interact with gas molecules and generate an acoustic signal. This acoustic signal is generated due to the photoacoustic effect. Step 3: One channel of the dual-channel function generator (9) provides a reference signal to the quadrature detector (4). The quadrature detector (4) extracts the phase fluctuation signal from the electrical signal output by the photodetector (3) and applies the phase fluctuation signal to the output of the two channels of the dual-channel function generator (9) through the phase shifter (10) to provide a reference signal to the lock-in amplifier (8). Step 4: The acoustic signal is converted into an electrical signal by the resonant acoustic-electric transducer (5) and amplified by the preamplifier (7). The amplified signal is then sent to the lock-in amplifier (8) for demodulation to obtain the phase-compressed dual-comb photoacoustic spectrum signal.

Images