A mid and far infrared mixing detection system with frequency sweeping splicing

Abstract

The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection. The application provides a swept splicing mid-far infrared mixing detection system and relates to the technical field of infrared detection.

Description

Technical Field

[0001] This invention relates to the field of infrared detection technology, and more specifically, to a mid-to-far infrared mixed-frequency detection system with frequency sweeping and splicing. Background Technology

[0002] Infrared detection technology is a detection technique applied to the infrared spectral range, typically from 0.78 to 1000 μm in wavelength. The mid- and far-infrared regions, with their longer wavelengths (>2.5 μm) compared to near-infrared and short-wave infrared, are of great significance in scientific research and practical applications. For example, mid- and far-infrared spectroscopy can provide detailed information about molecular chemical bonds, molecular structure, and vibrational dynamics. Researchers can analyze mid- and far-infrared spectra to study and understand molecular interactions, changes in molecular structure, and intramolecular vibrational modes, thereby gaining a deeper understanding of the properties of matter. Furthermore, the mid- and far-infrared region also has atmospheric transparency, making it suitable for environmental and air quality monitoring, climate research, and extraterrestrial object detection. For thermal radiation emitted by objects at room temperature, the majority of its energy spectrum is located in the mid- and far-infrared band; therefore, mid- and far-infrared detection technology is widely used in thermal imaging, infrared tracking, and guidance. Compared to the near-infrared and visible light bands, the sensitivity of mid- and far-infrared detectors is generally lower. The lower energy of mid- and far-infrared light necessitates detectors with higher sensitivity to obtain better measurement results. This can be a challenge for some low-signal-intensity applications. Frequency mixing detection is widely used in the detection of weak signals. It converts the signal light to be measured and the local oscillator light into a difference frequency with a lower frequency. This not only suppresses the interference of stray noise with a frequency significantly different from the local oscillator light, but also amplifies the intermediate frequency (IF) signal generated by the difference frequency, thus achieving higher sensitivity than direct detection. Frequency mixing detection requires a local oscillator light source with a frequency close to that of the signal light to be measured. However, compared to near-infrared and visible light, the performance of laser sources in the mid- and far-infrared bands is limited. Local oscillator linewidths are often wide, and due to limitations in the bandwidth of detectors, electronic spectrum analyzers, and other electronic equipment, the supported IF signal bandwidth may even be smaller than the linewidth of the local oscillator. This situation makes the detection of signal light very difficult, and the performance of the local oscillator severely restricts the application of frequency mixing detection technology in the mid- and far-infrared bands. Therefore, designing a mid- and far-infrared frequency mixing detection system that reduces the requirements for local oscillator linewidth and electronic device bandwidth is of great practical significance. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art or related technologies, and provides a mid- and far-infrared mixed frequency detection system with frequency sweeping and splicing, which has a wider mid- and far-infrared detection bandwidth, reduces the requirements for the local oscillator linewidth in mixed frequency detection, and can realize high-sensitivity broadband detection of mid- and far-infrared light under the condition of a wider local oscillator linewidth.

[0004] This invention is achieved through the following technical solution: a mid-to-far infrared mixing detection system using frequency sweeping and splicing, comprising: a local oscillator light source, the center frequency of which supports wide-spectrum tuning, has no narrow linewidth requirement, and can be used up to tens of GHz; an infrared beam combiner, used to combine the local oscillator light and the light to be measured into a single beam; a cryogenic container, used to provide a cryogenic environment, the cryogenic container having a light-entry window so that the beam emitted by the infrared beam combiner can enter the container; a filtering component, located inside the cryogenic container, corresponding to the light-entry window and receiving the incident beam, used to filter out background noise of the incident beam; a focusing component, located inside the cryogenic container, corresponding to the output end of the filtering component, used to converge the incident beam; and a mixing detector, located within the cryogenic container. Internally, it receives the converged beam emitted by the focusing component and converts the optical signal into an electrical signal; an isolator, located inside the cryogenic container, connects to a mixer detector at its input and an amplifier at its output to reduce echo interference in the circuit; an amplifier, located inside the cryogenic container, amplifies the power of the electrical signal; a spectrum analyzer, connected to the amplifier's output, detects the spectral information carried by the electrical signal; a control and calculation module, connected to the local oscillator and the spectrum analyzer, controls the local oscillator frequency, receives the current output optical frequency information from the local oscillator, receives the intermediate frequency information output by the spectrum analyzer, and splices the spectral information measured at different local oscillator frequencies to form an approximate broadband measurement result; the control and calculation module is configured as follows:

[0005] Determine the intermediate frequency ω of the overall measurement based on the measurement requirements. m The total number of segments N in the segmented splicing, where the total bandwidth of the equivalent measurement is B = 2ω m Then the measurement bandwidth for a single measurement is Δf = ω m / N, Δf is not greater than the maximum measurement bandwidth of the spectrum analyzer used in the measurement;

[0006] Controlling the center frequency of the output light from the local oscillator light source ensures that the frequency difference between the local oscillator light and the signal light, i.e., the intermediate frequency, is f. n (n = 1, 2, 3 ... N); where f1 = ω m f N =Δf, the frequency difference f between two adjacent intermediate frequency sequences n -f n+1 =Δf; Obtain and record the spectrum data within the Δf bandwidth of each intermediate frequency segment, that is, there are a total of N segments of spectrum data with a bandwidth of Δf;

[0007] The measured N segments of spectrum data are concatenated end-to-end to obtain the total measured spectrum data D; the intermediate frequency f of each segment is then concatenated. n The corresponding spectrum data is regarded as an array x n That is, D = [x1, x2, x3 ... x N Based on array D, plot the intermediate frequency ω.m The measurement results within the left half of the total equivalent measurement bandwidth B.

[0008] In this technical solution, the measurement scheme is carried out cyclically based on "measuring narrow bandwidth information - local oscillator offset - measuring narrow bandwidth information - local oscillator offset", and finally the narrow bandwidth spectrum is stitched together to achieve broadband measurement, thus avoiding the limitation of electronic bandwidth.

[0009] The mid-to-far infrared mixing detection system with frequency sweeping splicing provided by the present invention preferably further includes: an electronic filter, disposed between the amplifier and the spectrum analyzer, for improving the signal-to-noise ratio of the electrical signal and reducing the inherent noise inside the circuit.

[0010] In the mid-to-far infrared mixed-frequency detection system with frequency sweeping and splicing provided by the present invention, the cryogenic container is preferably a Dewar jar.

[0011] According to the mid-to-far infrared mixed-frequency detection system with frequency sweeping and splicing provided by the present invention, preferably, the coupling antenna of the mixed-frequency detector is designed according to the wavelength of the signal light to be measured in order to enhance the coupling efficiency of light energy.

[0012] According to the frequency sweeping and splicing mid- and far-infrared mixing detection system provided by the present invention, preferably, the mixing detector includes: a superconducting thermal electron thermometric radiometer or a superconducting nanowire single-photon detector.

[0013] In the mid-to-far infrared mixing detection system with frequency sweeping splicing provided by the present invention, preferably, the measurement bandwidth of the spectrum analyzer is matched with the bandwidth of the mixing detector, isolator, amplifier, electronic filter and electrical signal wire.

[0014] The beneficial effects achieved by this invention include at least the following: based on the above-disclosed technical solution, the linewidth requirement of the local oscillator source is reduced, and the acquisition cost of related equipment and devices is lower; based on the tunable local oscillator source, multi-segment measurement is performed, and the approximate power spectrum of the signal light is obtained by frequency sweeping splicing. The more segments, the better the restoration effect of the actual power spectrum. Even if the linewidth of the local oscillator source is greater than the intermediate frequency or the bandwidth of the electronic device is less than the intermediate frequency, a high-precision detection result can still be achieved. Attached Figure Description

[0015] Figure 1 A schematic diagram of a mid-to-far infrared mixing detection system based on a frequency sweeping and splicing method according to an embodiment of the present invention is shown.

[0016] Figure 2 The theoretical power spectrum corresponding to different intermediate frequency frequencies is shown according to an embodiment of the present invention, taking into account the linewidth of the signal light and the local oscillator source.

[0017] Figure 3 The simulation results are shown in the figure according to an embodiment of the present invention. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, this invention provides a mid-to-far infrared mixing detection system with frequency sweeping and splicing, comprising: an infrared beam combiner (1), a local oscillator light source (2), a cryogenic container (3), a light-gathering window (4), a filter assembly (5), a focusing assembly (6), a mixing detector (7), an isolator (8), an amplifier (9), an electronic filter (10), a spectrum analyzer (11), and a control and calculation module (12). The cryogenic container can be a Dewar flask, and the control and calculation module is configured as follows:

[0020] Step 1: Determine the intermediate frequency ω for the overall measurement based on the measurement requirements. m The total number of segments N in the segmented splicing, where the total bandwidth of the equivalent measurement is B = 2ω m The bandwidth should be no less than twice the sum of the widths of the signal light and the local oscillator light, and the total number of segments should generally be no less than 50. Therefore, the measurement bandwidth for a single measurement is Δf = ω. m / N, Δf is not greater than the maximum measurement bandwidth of the spectrum analyzer used in the measurement.

[0021] Step 2: Adjust the center frequency of the local oscillator output light so that the frequency difference between the local oscillator light and the signal light, i.e., the intermediate frequency, is f. n (n = 1, 2, 3...N). Where, f1 = ω m f N =Δf, the frequency difference f between two adjacent intermediate frequency sequences n -f n+1 =Δf. The spectrum data within the bandwidth of Δf at each intermediate frequency is measured using a spectrum analyzer and acquired and recorded by the control calculation module. There are a total of N spectrum data segments with a bandwidth of Δf.

[0022] Step 3: The data is processed by the control and calculation module. The N measured spectrum data segments are concatenated end-to-end to obtain the total measured spectrum data D. The intermediate frequency f of each segment is then processed. n The corresponding spectrum data is regarded as an array x n That is, D = [x1, x2, x3 ... x N Based on array D, the intermediate frequency ω can be plotted. m The measurement results are then taken within the left half of the total bandwidth B, which is equivalent to the measurement time. At this point, the high-frequency intermediate frequency ω, which cannot be measured in traditional mixing measurements, is obtained. m The spectrum measurement was reduced to a spectrum measurement of N segments with a bandwidth of only Δf.

[0023] In this embodiment, the infrared signal light to be measured and the local oscillator light are combined into a single beam by an infrared beam combiner. This beam enters the cryogenic Dewar flask through the light-inlet window. It then passes through a filtering component and a focusing component, ultimately focusing the infrared light energy onto a mixer detector. The intermediate frequency signal generated by mixing the signal with the local oscillator light is responded to by the mixer detector and converted into an electrical signal. This electrical signal passes through an isolator and an amplifier before exiting the Dewar flask. After electronic filtering, it is finally received by a spectrum analyzer. The control and calculation module is connected to the local oscillator light source and the spectrum analyzer via electrical signal paths. Through programmed control, the output frequency of the local oscillator light is scanned, and the power spectrum measured by the spectrum analyzer at different local oscillator light frequencies is recorded. Finally, by stitching together multiple sets of power spectrum data at different local oscillator light frequencies, an approximate single-shot broadband measurement result can be obtained, thereby reducing the requirements for device bandwidth and local oscillator source linewidth in the mixer detection.

[0024] According to the above embodiments, preferably, the infrared beam combiner, light-entry window, optical filter, and focusing lens should be selected based on the wavelength of the signal light to be measured, using materials and coatings accordingly. For example, fluoride materials can be selected for the signal light to be measured in the 2-7 μm range, germanium materials can be selected for the 7-12 μm range, and silicon, polytetrafluoroethylene, or other materials can be selected for the terahertz band. The optical filter is used to filter out background noise in the light field that is not in the measured wavelength range, and the focusing lens is used to converge the light field onto the detector coupling antenna.

[0025] According to the above embodiments, preferably, the filtering component, focusing component, mixer detector, isolator, and amplifier should be placed inside a cryogenic Dewar flask to reduce background noise caused by the thermal radiation of the devices themselves, while ensuring that the mixer detector operates at the optimal temperature and improving the detection sensitivity of the system. The isolator is used to prevent circuit echoes from affecting the detection device, and the amplifier is used to amplify the detected electrical signal and improve the signal strength.

[0026] According to the above embodiments, preferably, the coupling antenna of the mixer detector needs to be designed according to the wavelength of the signal light to be measured in order to enhance the coupling efficiency of light energy. The mixer detector can be a superconducting thermal electron thermometry radiometer, a superconducting nanowire photon detector, or other detectors with ultra-high sensitivity.

[0027] According to the above embodiments, preferably, the electronic filter is used to filter out noise from the amplifier and improve the signal-to-noise ratio of the system. The measurement bandwidth of the spectrum analyzer needs to match the bandwidth of electronic components in the system, such as the mixer detector, isolator, amplifier, electronic filter, and electrical signal wires, and is generally not less than 7 GHz.

[0028] According to the above embodiments, the optical path of the present invention includes a local oscillator light source, a signal light under test, an infrared beam combiner, a filtering component, a focusing component, and a mixer detector. The local oscillator light emitted by the local oscillator light source and the signal light under test are combined into a single beam by the infrared beam combiner, enter the Dewar jar through the light inlet window, first pass through an optical filter to remove background noise in the non-signal light frequency band, and finally be focused onto the coupling antenna of the mixer detector by a focusing lens. The mixer detector converts the mixed intermediate frequency signal into an electrical signal. The electrical signal path of the present invention includes an isolator, an amplifier, an electronic filter, a spectrum analyzer, and a control and calculation module. Specifically, the electrical signal generated by the mixer detector passes sequentially through the isolator, amplifier, and electronic filter before being received by the spectrum analyzer to obtain the spectrum information of the electrical signal. The local oscillator light source and the spectrum analyzer are connected to the control and calculation module through the electrical signal path. The local oscillator light source receives control signals from the control and calculation module for tuning, and the spectrum analyzer can send relevant data information to the control and calculation module. The isolator and amplifier are placed inside the Dewar jar to reduce their noise levels. Isolators effectively prevent echo interference in the circuit, improving the detector's sensitivity. Amplifiers amplify the power of electrical signals, enhancing the detection capability of weak signals. Electronic filters improve the signal-to-noise ratio of electrical signals and reduce inherent noise within the circuit. The control and calculation module controls the local oscillator and spectrum analyzer to acquire, stitch, and ultimately present the detection results.

[0029] When considering the phase noise of the optical field, i.e., its linewidth, the electric field intensity E can be expressed as:

[0030]

[0031] In the formula, E0 and ω m φ(t) represents the amplitude, frequency, and time-dependent phase of the light field, respectively.

[0032] Suppose that the random phase jumps follow a Gaussian distribution with a mean of zero, i.e., the light field has a Lorentz-linear spectral width, then...

[0033]

[0034] In the formula, Δφ(t,τ)=φ(t+τ)-φ(t), and Δω is the linewidth of the light field.

[0035] Let the frequencies and linewidths of the signal light and the local oscillator light be ω and ω, respectively. s ω L With Δω s , Δω L Substituting the electric field intensity expression considering the linewidth of the optical field into the intermediate frequency signal of the mixing response, the final power spectral density G(ω) is related to the optical field frequency and linewidth as follows:

[0036]

[0037] In the formula, ω m For the intermediate frequency, ω m =|ω L -ω s Based on this formula, the intermediate frequency spectrum of the optical field with linewidth can be calculated without considering noise. In practical applications, electronic devices have operating bandwidths, and for common mixer detectors, the maximum frequency they can respond to is generally less than 10 GHz. For signals with linewidths greater than 10 GHz and for local oscillator light, existing measurement methods are almost unable to obtain effective information.

[0038] According to such Figure 2 The diagram shows the theoretical power spectra corresponding to different intermediate frequency (IF) frequencies, considering the linewidths of the signal light and the local oscillator. Assuming no upper limit on the system's operating frequency and a linewidth of 50 GHz for both the signal light and the local oscillator, the theoretical IF power spectrum is insufficient to obtain useful measurement information at the same IF frequency of 50 GHz. Measurement is only meaningful when the IF frequency is significantly greater than the linewidths of the signal light and the local oscillator. However, due to limitations in the operating bandwidth of electronic devices, high-frequency spectra are impossible to measure in practical experiments. Therefore, this invention proposes scanning the IF frequency to measure the low-frequency power spectrum in a single measurement, then stitching together multiple spectral data segments to approximate the entire spectrum.

[0039] like Figure 3 As shown, one embodiment of the present invention takes 100 segments spliced ​​together as an example. The intermediate frequency (IF) is changed by 10 GHz in a single step, i.e., the tunable local oscillator is scanned, changing the frequency difference between its optical frequency and the frequency of the signal light under test by 10 GHz. The power spectrum below 10 GHz under this IF condition is measured using a spectrum analyzer. The IF is changed sequentially from 10 GHz to 1000 GHz, a total of 100 times, acquiring 100 sets of power spectra below 10 GHz. These 100 sets of power spectrum data are then spliced ​​in reverse to obtain the measurement result. Figure 2 It is known that the lower the intermediate frequency, the greater the power spectrum distortion at low frequencies. Therefore, the power spectrum distortion is more pronounced closer to 1000 GHz in the splicing process. However, from... Figure 3 As can be seen, the more segments there are, the smaller the impact of this distortion becomes. Ultimately, more accurate and effective measurement results can be obtained.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A mid-to-far infrared frequency mixing detection system with frequency sweeping and splicing, characterized in that, include: Local oscillator light source, wherein the center frequency of the local oscillator light source supports wide-spectrum tuning and has no narrow linewidth requirement; An infrared beam combiner is used to combine the local oscillator light and the signal light to be measured into a single beam. A cryogenic container for providing a cryogenic environment, the cryogenic container having a light-entry window to allow a light beam emitted by the infrared beam combiner to enter the container interior; A filtering component is disposed inside the cryogenic container, corresponding to the light-inlet window and receiving the incident light beam, for filtering out the background noise of the incident light beam; A focusing component is located inside the cryogenic container and is positioned corresponding to the output end of the filtering component to converge the incident light beam. A mixer detector, located inside the cryogenic container, receives the focused light beam emitted by the focusing component and converts the optical signal into an electrical signal; An isolator, located inside the cryogenic container, has its input connected to the mixer detector and its output connected to an amplifier, used to reduce echo interference in the circuit. The amplifier is located inside the cryogenic container and is used to amplify the power of the electrical signal; A spectrum analyzer, connected to the output of the amplifier, is used to detect the spectral information carried by the electrical signal; The control and calculation module is connected to the local oscillator light source and the spectrum analyzer. It is used to control the local oscillator light frequency of the local oscillator light source, receive the optical frequency information currently output by the local oscillator light source, receive the intermediate frequency information output by the spectrum analyzer, and splice the spectrum information measured at different local oscillator light frequencies to form an approximate broadband measurement result. The control and calculation module is configured as follows: Determine the intermediate frequency ω of the overall measurement m The total number of segments N in the segmented splicing, where the total bandwidth of the equivalent measurement is B = 2ω m Then the measurement bandwidth for a single measurement is Δf = ω m / N, Δf is not greater than the maximum measurement bandwidth of the spectrum analyzer used in the measurement; Controlling the center frequency of the output light from the local oscillator light source ensures that the frequency difference between the local oscillator light and the signal light, i.e., the intermediate frequency, is f. n (n = 1, 2, 3 ... N); where f1 = ω m f N =Δf, the frequency difference f between two adjacent intermediate frequency sequences n -f n+1 =Δf; Obtain and record the spectrum data within the Δf bandwidth of each intermediate frequency segment, that is, there are a total of N segments of spectrum data with a bandwidth of Δf; The measured N segments of spectrum data are concatenated end-to-end to obtain the total measured spectrum data D; the intermediate frequency f of each segment is then concatenated. n The corresponding spectrum data is regarded as an array x n That is, D = [x1, x2, x3 ... x N Based on array D, plot the intermediate frequency ω. m The measurement results within the left half of the total equivalent measurement bandwidth B.

2. The mid-to-far infrared mixing detection system with frequency sweeping and splicing according to claim 1, characterized in that, Also includes: An electronic filter, located between the amplifier and the spectrum analyzer, is used to improve the signal-to-noise ratio of the electrical signal and reduce the inherent noise within the circuit.

3. The mid-to-far infrared mixing detection system with frequency sweeping and splicing according to claim 1, characterized in that, The cryogenic container is a Dewar jar.

4. The mid-to-far infrared mixing detection system with frequency sweeping and splicing according to claim 1, characterized in that, The coupling antenna of the mixer detector is designed according to the wavelength of the signal light to be measured in order to enhance the coupling efficiency of light energy.

5. The mid-to-far infrared mixing detection system with frequency sweeping and splicing according to claim 4, characterized in that, Mixer detectors include: superconducting thermal electron thermometry or superconducting nanowire single-photon detectors.

6. The mid-to-far infrared mixing detection system with frequency sweeping and splicing according to claim 2, characterized in that, The measurement bandwidth of the spectrum analyzer is matched with the bandwidth of the mixer detector, the isolator, the amplifier, the electronic filter, and the electrical signal conductor.

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