TDLAS and electro-optical modulator based single sideband modulation gas detection method and system

Abstract

The application discloses a single sideband modulation gas detection method and system based on TDLAS and an electro-optic modulator, and belongs to the technical field of gas concentration detection. The method comprises the following steps: inputting a laser beam of a specific wavelength emitted by a laser into an electro-optic modulator, and driving the electro-optic modulator by a radio frequency signal; inputting the laser beam is modulated into output light containing a carrier frequency and two sideband frequencies by the electro-optic modulator; the output light is subjected to single sideband modulation by an optical filter to obtain single sideband laser corresponding to an absorption line of a gas to be detected; the single sideband laser is guided into a gas region to be detected and reflected to a detector; the reflected light signal is converted by an electronic circuit, and the output electric signal is subjected to data processing to obtain the gas concentration of the gas to be detected. The application can realize fast modulation and response, and has the advantages of high precision and high reliability.

Description

Technical Field

[0001] This invention relates to the field of gas concentration detection technology, and more specifically to a single-sideband modulated gas detection method and system based on TDLAS and an electro-optic modulator. Background Technology

[0002] Currently, traditional gas concentration measurement methods often suffer from problems such as low accuracy, poor reliability, long response time, and complex systems that cannot be integrated. To overcome these problems, TDLAS technology has been widely used.

[0003] However, in existing TDLAS-based laser gas sensor designs, a key challenge is achieving high-speed modulation, which is crucial for applications requiring rapid response, such as online monitoring and respiration analysis.

[0004] Therefore, how to provide a gas sensing method and system that can achieve rapid modulation and response while having high accuracy and high reliability is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a single-sideband modulated gas detection method and system based on TDLAS and an electro-optic modulator.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, this invention discloses a single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator, comprising the following steps:

[0008] A laser beam of a specific wavelength emitted by a laser is input into an electro-optic modulator, which is driven by a radio frequency signal;

[0009] The input laser beam is modulated by an electro-optic modulator into an output light containing one carrier frequency and two sideband frequencies;

[0010] The output light is modulated by a single-sideband optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas under test.

[0011] The single-sideband laser is guided into the region of the gas to be measured and reflected to the detector.

[0012] The reflected light signal of the single-sideband laser is converted and regulated by the electronic circuit of the detector, and then output as an electrical signal.

[0013] The electrical signal is processed to obtain the gas concentration of the gas to be measured.

[0014] Furthermore, the laser includes a distributed feedback laser or a quantum cascade laser.

[0015] Furthermore, the laser is stably emitted by controlling the current and temperature.

[0016] Furthermore, the electro-optic modulator modulates the input laser beam by controlling the refractive index of an electric field control material, wherein the electric field control material includes lithium niobate.

[0017] Furthermore, the electrical signal is processed to obtain the gas concentration of the gas to be tested. Specifically, this includes using peak detection, integral absorption, and fitting algorithms to analyze the absorption characteristics of a single-sideband laser after passing through the gas sample to be tested, and calculating the concentration of the gas sample to be tested based on the absorption characteristics of the gas sample to be tested.

[0018] On the other hand, the present invention also discloses a single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator, including a laser, an opto-modulator, a control system, optical components, a receiver, and a signal processing system;

[0019] The laser is used to emit a laser beam of a specific wavelength;

[0020] The electro-optic modulator is used to modulate the input laser beam into an output light containing one carrier frequency and two sideband frequencies, and to perform single-sideband modulation through an optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas under test.

[0021] The control system is used to generate radio frequency signals, which are used to drive the electro-optic modulator.

[0022] The optical components are used to ensure that the output single-sideband laser passes through the gas sample in the gas region to be tested along a predetermined path;

[0023] The detector is used to receive light signals that pass through the gas sample to be tested and are reflected by the reflective surface, and to convert the light signals into electrical signals.

[0024] The signal processing system is used to process and analyze the electrical signals output by the detector to extract gas absorption information and calculate the gas concentration of the gas sample to be tested.

[0025] Preferably, the laser includes a distributed feedback laser or a quantum cascade laser.

[0026] Preferably, the control system is also used to ensure that the laser emits a stable laser beam by controlling the current and temperature.

[0027] Preferably, the electro-optic modulator modulates the input laser beam by controlling the refractive index of an electric field control material, wherein the electric field control material includes lithium niobate.

[0028] Preferably, the signal processing system extracts gas absorption information and calculates the gas concentration of the gas sample to be tested. Specifically, it uses peak detection, integral absorption, and fitting algorithms to analyze the absorption characteristics of a single-sideband laser after passing through the gas sample to be tested, and calculates the concentration of the gas sample to be tested based on the absorption characteristics of the gas sample to be tested.

[0029] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a single-sideband modulated gas detection method and system based on TDLAS and electro-optic modulator, which has the following beneficial effects:

[0030] This invention facilitates more accurate spectral analysis through single-sideband modulation, while the use of an electro-optic modulator enables rapid modulation, enhancing the system's responsiveness to rapidly changing concentrations, which is particularly important for industrial processes requiring rapid monitoring and adjustment.

[0031] This invention combines TDLAS technology with an electro-optic modulator to achieve single-sideband modulation, thereby eliminating the need for complex modulation and demodulation equipment, simplifying system design and reducing reliance on complex demodulation algorithms. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the overall steps of the single-sideband modulated gas detection method provided by the present invention.

[0034] Figure 2 This is a schematic diagram of the single-sideband modulated gas detection system provided by the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention first discloses a single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator, such as... Figure 1 As shown, the method includes the following steps: inputting a laser beam of a specific wavelength emitted by a laser into an electro-optic modulator, wherein the electro-optic modulator is driven by a radio frequency signal;

[0037] The input laser beam is modulated by an electro-optic modulator into an output light containing one carrier frequency and two sideband frequencies;

[0038] The output light is modulated by a single-sideband optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas under test.

[0039] A single-sideband laser is guided into the region of the gas to be measured and reflected back to the detector.

[0040] The reflected light signal of the single-sideband laser is converted and regulated by the electronic circuit of the detector, and then output as an electrical signal.

[0041] The gas concentration of the gas to be measured is obtained after data processing of the electrical signal.

[0042] This invention also discloses a single-sideband modulated gas detection system based on TDLAS and an electro-optic modulator, such as... Figure 2 As shown, the system includes a laser, an optoelectronic modulator, a control system, an optical lens, a receiver, and a signal processing system. The laser emits a laser beam of a specific wavelength. The optoelectronic modulator modulates the input laser beam into an output light containing one carrier frequency and two sideband frequencies, and performs single-sideband modulation through an optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas to be tested. The control system generates a radio frequency signal to drive the optoelectronic modulator. Optical components ensure that the output single-sideband laser passes through the gas sample in the gas region according to a predetermined path. A detector receives the light signal that passes through the gas sample and is reflected by a reflective surface, and converts the light signal into an electrical signal. The signal processing system processes and analyzes the electrical signal output by the detector to extract gas absorption information and calculate the gas concentration of the gas sample.

[0043] In the above system, the control system also ensures that the laser emits a stable laser beam by controlling the current and temperature.

[0044] This invention employs a combination of tunable laser absorption spectroscopy (TDLAS) technology and an electro-optic modulator (EOM) to achieve single-sideband modulation, which features high sensitivity, high selectivity, and fast response.

[0045] The inventive principles of the present invention will be further explained below with reference to more specific embodiments.

[0046] In the methods and systems of this invention, the laser used to emit the laser beam is a tunable laser, such as a distributed feedback laser (DFB) or a quantum cascade laser (QCL), capable of generating a beam of a specific wavelength. These wavelengths are typically selected as wavelengths of the absorption spectral lines of the target gas.

[0047] An electro-optic modulator (EOM) modulates light waves by controlling the refractive index of a material using an electric field. This enables single-sideband modulation of the light wave, selecting only the sideband corresponding to the absorption line of the target gas while suppressing or excluding other sidebands. In one specific embodiment, the power control material of the electro-optic modulator (EOM) can be lithium niobate (LiNbO3) or GaAs (gallium arsenide).

[0048] In one specific embodiment, the electro-optic modulator modulates the input laser beam by means of a method that adjusts the phase of the input laser wave by rapidly changing the electric field, thereby indirectly affecting the frequency.

[0049] To improve the modulation efficiency of the electro-optic modulator, in one specific embodiment, the modulation voltage of the electro-optic modulator can be changed by the driving circuit to improve the modulation efficiency.

[0050] In this embodiment of the invention, the radio frequency (RF) signal driving the optoelectronic modulator is generated by the control system. The frequency and amplitude of the RF signal determine the characteristics of the generated sideband. In this invention, it is necessary to ensure that the main frequency is suppressed and the required single-sideband laser is enhanced. The frequency of the RF signal can be calculated based on the wavelength of the laser, and is generally set to 10^6-10^8 Hz.

[0051] A single-sided laser passes through an optical assembly and then through the gas sample to be tested. The optical assembly typically consists of a varying number of optical lenses and optical fibers, which are used to ensure that the single-sided laser passes through the gas sample to be tested along a specific path.

[0052] In this invention, a detector is used to receive light signals that pass through and are reflected from the gas sample to be tested, and converts the light signals into electrical signals; a signal processing system is used to process and analyze the electrical signals output by the detector to extract gas absorption information and calculate the gas concentration of the gas sample to be tested.

[0053] In this invention, the gas sample to be tested is located in a gas sample bag or gas flow chamber and is reflected by a reflective surface. The reflective surface is generally a gold-plated mirror, which has the advantages of high reflectivity and corrosion resistance.

[0054] The detector senses changes in light intensity and converts these changes into electrical signals. The choice of detector depends on the wavelength range of the light to be detected. Specifically, the detector uses a photodiode (PD) or an avalanche photodiode (APD) and corresponding cross-amplifier circuitry to convert the detected light signal into a voltage or current signal, which is then input into a signal processing system for processing and analysis to obtain the gas concentration of the gas sample.

[0055] In one specific embodiment, the signal processing system uses peak detection, integral absorption, and fitting algorithms to analyze the absorption characteristics of the laser after passing through a gas sample, and uses the Beer-Lambert law to obtain the concentration of the gas to be detected.

[0056] In this invention, the control system, in addition to generating radio frequency signals, can also ensure stable laser emission by controlling current and temperature. Specifically, the control system can control the laser output through frequency locking technology. First, the detected optical signal is converted into a voltage signal and input to a coherent demodulator (such as a lock-in amplifier) ​​for processing, extracting a specific component (error signal) of the frequency modulation signal. Then, a feedback signal is generated using the error signal and sent back to the laser's control circuit to adjust the laser frequency in real time, thereby stably locking the laser frequency at the desired reference frequency.

[0057] This invention provides an effective technical approach for real-time gas detection by combining TDLAS and an electro-optic modulator to achieve single-sideband modulation. It has broad application prospects in fields such as petrochemicals, environmental monitoring, and medical diagnostics.

[0058] In general, in this invention, the laser emitted from the laser beam passes through an EOM (External Optical Array) via a transmission optical fiber. The EOM is driven by a radio frequency signal with a frequency set to 10^6-10^8 Hz. Through the EOM, the laser beam is modulated into light containing multiple frequency components, primarily a carrier frequency and two sideband frequencies. The light generated using the EOM passes through an optical filter, such as a fiber grating, to suppress one sideband, allowing only one modulated sideband to pass. This achieves single-sideband modulation, with the retained sideband having a frequency equal to or less than the modulation frequency of the initial laser frequency. The selected single-sideband laser is guided through a region containing a target gas. When the frequency of the laser beam coincides with a specific absorption line of the target gas, the beam is absorbed by the gas molecules. The laser beam passing through the gas absorption region is reflected onto a detector. Due to absorption, the intensity of the transmitted light decreases, and this change in intensity is proportional to the gas concentration. The detector's output signal is demodulated by electronic circuitry to obtain gas concentration information. The acquired signal is amplified, filtered, and digitized, and the gas concentration is calculated using a data processing algorithm. Data processing algorithms take into account the effects of parameters such as background signals, temperature changes, and pressure changes to improve the accuracy and stability of measurements.

[0059] An optical filter is an independent passive fiber optic device that is connected to the EOM via optical fiber. Light travels from the laser through the optical fiber to the EOM, then through the optical fiber to the filter, and finally through the optical fiber to the lens in the optical assembly before exiting.

[0060] The optical fibers are all encapsulated in each device. In this sensor, the laser, electro-optic modulator, and lens are all connected by optical fibers without the need for connectors. Generally, the encapsulated optical fibers that come with each device are connected by fusion splicing, and finally, the optical fibers are connected to the lens using the optical fiber connector on the lens.

[0061] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator, characterized in that, Includes the following steps: A laser beam of a specific wavelength emitted by a laser is input into an electro-optic modulator, which is driven by a radio frequency signal; The input laser beam is modulated by an electro-optic modulator into an output light containing one carrier frequency and two sideband frequencies; The output light is modulated by a single-sideband optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas under test. The single-sideband laser is guided into the region of the gas to be measured and reflected to the detector. The reflected light signal of the single-sideband laser is converted and regulated by the electronic circuit of the detector, and then output as an electrical signal. The electrical signal is processed to obtain the gas concentration of the gas to be measured.

2. The single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator according to claim 1, characterized in that, The laser includes distributed feedback lasers or quantum cascade lasers.

3. The single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator according to claim 1, characterized in that, The laser emits a stable laser beam by controlling the current and temperature.

4. The single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator according to claim 1, characterized in that, The electro-optic modulator modulates the input laser beam by controlling the refractive index of an electric field-controlled material, which includes lithium niobate.

5. The single-sideband modulated gas detection method based on TDLAS and an electro-optic modulator according to claim 1, characterized in that, The electrical signal is processed to obtain the gas concentration of the gas to be tested. Specifically, peak detection, integral absorption and fitting algorithms are used to analyze the absorption characteristics of a single-sideband laser after passing through the gas sample to be tested, and the concentration of the gas sample to be tested is calculated based on the absorption characteristics of the gas sample to be tested.

6. A single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator, characterized in that, This includes lasers, optoelectronic modulators, control systems, optical components, receivers, and signal processing systems; The laser is used to emit a laser beam of a specific wavelength; The electro-optic modulator is used to modulate the input laser beam into an output light containing one carrier frequency and two sideband frequencies, and to perform single-sideband modulation through an optical filter to obtain a single-sideband laser corresponding to the absorption line of the gas under test. The control system is used to generate radio frequency signals, which are used to drive the electro-optic modulator. The optical components are used to ensure that the output single-sideband laser passes through the gas sample in the gas region to be tested along a predetermined path; The receiver is used to receive the light signal that passes through the gas sample to be tested and is reflected by the reflective surface, and to convert the light signal into an electrical signal. The signal processing system is used to process and analyze the electrical signals output by the detector to extract gas absorption information and calculate the gas concentration of the gas sample to be tested.

7. The single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator according to claim 6, characterized in that, The laser includes distributed feedback lasers or quantum cascade lasers.

8. The single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator according to claim 6, characterized in that, The control system is also used to ensure that the laser emits a stable laser beam by controlling the current and temperature.

9. The single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator according to claim 6, characterized in that, The electro-optic modulator modulates the input laser beam by controlling the refractive index of an electric field-controlled material, which includes lithium niobate.

10. The single-sideband modulated gas sensing system based on TDLAS and an electro-optic modulator according to claim 6, characterized in that, The signal processing system extracts gas absorption information and calculates the gas concentration of the gas sample to be tested. Specifically, it uses peak detection, integral absorption, and fitting algorithms to analyze the absorption characteristics of a single-sideband laser after passing through the gas sample to be tested, and calculates the concentration of the gas sample to be tested based on the absorption characteristics of the gas sample to be tested.

Images