A frequency-shifting filtering spectral measurement method and system based on a modulated microcavity optical frequency comb

Abstract

The present invention provides a frequency-shifted filtering spectral measurement method and system based on a modulated microcavity optical frequency comb, belonging to the field of spectral precision measurement, including a chip-integrated microcavity optical frequency comb of a light source, an electro-optic modulator, an optical fiber FP filter, a piezoelectric drive controller, an optical switch, a first test optical path or a second test optical path, a second fiber coupler, and a photodetector. By adopting the above-mentioned frequency-shifted filtering spectral measurement method and system based on a modulated microcavity optical frequency comb, the present invention can give play to the advantages of miniaturization and high spectral resolution of the chip optical comb, and is utilized in gas monitoring and open atmosphere gas monitoring, and is expected to be widely applied in the fields of environmental protection, climate, industrial safety, etc.

Description

Technical Field

[0001] The present invention belongs to the field of precision spectral measurement, and in particular, relates to a frequency-shifted filtering spectral measurement method and system based on a modulated microcavity optical comb. Background Art

[0002] By measuring the steady-state spectrum with a grating spectrometer, the information of the spectrum of the measured gas can be intuitively displayed, which has greatly promoted the development of high-resolution spectral detection technology. However, its measurement rate in the order of Hz means that some important dynamic processes may be missed, and the current manufacturing process limits its resolution to the order of GHz. The recently developed mode-locked dual-comb spectroscopy technology has a repetition frequency in the order of MHz and can achieve high-speed dynamic spectral characterization. However, its high cost and complex system settings limit its application outside the laboratory. The generation of a microcavity optical comb only requires coupling the pump light into an optical microcavity to generate stable optical comb pulses. If the pump light wavelength is further stabilized to a reference source (such as a high-stability etalon), the frequency stability of the microcavity optical comb can also reach the effect of a mode-locked optical comb, which lays a foundation for field experiments at the Hz level. Compared with dispersive and interferometric spectrometers, an optical fiber FP filter based on the Fabry-Perot interferometer principle with a higher scanning rate and resolution has the potential to achieve high-precision real-time characterization of the high-resolution spectrum of a microcavity optical frequency comb light source.

[0003] An electro-optic modulator can generate sidebands on both sides of the input carrier, and the frequency difference relative to the carrier is the magnitude of the modulation frequency. An IQ modulator based on a dual-parallel Mach-Zehnder modulator can suppress the carrier and a certain sideband. By reasonably setting the operating point and bias voltage of the modulator, dynamic tuning of the single sideband can be achieved by only changing the bias point of one of the modulators. Since the generation of the single sideband is closely related to the carrier, the stability of the single sideband can be achieved by stabilizing the frequency of the carrier (i.e., the teeth of the original microcavity optical comb). At this time, by stepping the modulation frequency across the entire comb tooth interval, the single sideband coverage in the entire spectral range can be achieved. An optical fiber FP filter is a resonator made based on the multi-beam interference principle. The FP cavity consists of two parallel plates coated with high-reflectivity films. The light beam in the optical fiber is directly input into the cavity and reflected multiple times between the two mirrors, forming narrow-band transmission peaks in the spectrum. By changing the voltage applied to the piezoelectric ceramic, the cavity length can be tuned to control the center wavelength of the transmission peak.

[0004] The classical FP resonator consists of two plates with surfaces of high-reflectivity thin films, as Figure 2 shown, and for details, reference can be made to "Optics" compiled by You Pu and Yu Guoping in July 2003 and published in July 2003. Summary of the Invention

[0005] The object of the present invention is to provide a frequency-shifted filtering spectral measurement method and system based on a modulated microcavity optical comb. By modulating the intensity of the teeth of the input microcavity optical comb signal and its generated sidebands through an IQ electro-optic modulator, suppressing the carrier wave and another sideband, and then measuring the signal filtered by a high-speed scanning fiber Fabry-Perot (FP) cavity with a photodetector, the single-sideband teeth generated by changing the modulation frequency can be swept across the spectral range of the entire microcavity optical comb, and a spectral resolution at the level of the tooth linewidth can be obtained.

[0006] To achieve the above object, the present invention provides a frequency-shifted filtering spectral measurement system based on a modulated microcavity optical comb, which sequentially includes a light source, an IQ electro-optic modulator, a fiber FP filter, a piezoelectric drive controller, an optical switch, a first test optical path or a second test optical path, a second fiber coupler, and a photodetector.

[0007] Preferably, the first test optical path includes a gas cell to be measured, and the two ends of the gas cell to be measured are respectively connected to an optical switch and a photodetector.

[0008] Preferably, the second test optical path includes a light source to be measured, a first fiber coupler, and a low-pass filter; the light source to be measured is connected to the first fiber coupler, and the two ends of the first fiber coupler are respectively connected to an optical switch and a low-pass filter, and the low-pass filter is connected to the second fiber coupler.

[0009] Preferably, an FP cavity is provided in the fiber FP filter, and after the FP cavity scans one cycle, the modulation frequency of the signal source is increased by one step.

[0010] Preferably, the light source, the IQ electro-optic modulator, the fiber FP filter, the piezoelectric drive controller, the optical switch, the first test optical path or the second test optical path, the second fiber coupler, and the photodetector are sequentially connected by optical fibers.

[0011] Preferably, an amplifier can be added between the fiber FP filter and the optical switch;

[0012] Or an amplifier can be added between the light source and the IQ electro-optic modulator.

[0013] Preferably, the light source is emitted by a chip-integrated microcavity optical frequency comb.

[0014] A frequency-shifted filtering spectral measurement method based on a modulated microcavity optical comb uses a chip-integrated microcavity optical frequency comb to emit a light beam. The light beam passes through an IQ electro-optic modulator to generate a single-sideband output signal with carrier sideband suppression. The single-sideband output signal passes through a fiber FP filter to sequentially filter out the signals at each center wavelength and enters the optical switch;

[0015] When the optical switch is placed in the first test optical path, it is used to detect the absorption spectrum of the gas sample to be measured: The light filtered by the FP cavity passes through the optical switch and the gas cell to be measured. The component at the corresponding absorption line is absorbed, and the signal after absorption attenuation is received by the photodetector;

[0016] When the optical switch is placed in the second test optical path, it is used to detect the unknown signal spectrum: The light filtered by the FP cavity and the light to be measured are combined to generate a beat frequency under the action of the first fiber coupler. The signal less than half of the repetition frequency is filtered out by the low-pass filter, and the spectral signal is received by the photodetector, and the unknown signal spectrum is obtained by inversion;

[0017] The second fiber coupler combines the first test optical path and the second test optical path, and shares a photodetector. Only the first test optical path or the second test optical path works in a single test; The beam emitted by the light source to be measured enters the first fiber coupler and is combined with the signals at each center wavelength. The combined signal low-pass filter is used to suppress high-frequency noise and interference signals;

[0018] The photodetector receives the combined beam.

[0019] Therefore, the present invention adopts the above-mentioned frequency-shifted filtering spectral measurement method and system based on a modulated microcavity optical comb, and the technical effects are as follows:

[0020] (1) The single-sideband output of the beam emitted by the chip optical comb light source modulated by the IQ electro-optic modulator passes through the fiber FP filter and cooperates with the photodetection system to receive the narrow linewidth signal in the transmission passband. The signal magnitude of the detector under the corresponding voltage can be directly read out, and then the modulation frequency is stepped to obtain the spectral information within the entire chip optical comb spectral width in the single-sideband frequency-shifting manner, and fast absorption spectral measurement can be realized.

[0021] (2) There is strong coherence between the teeth of the chip optical comb. For an unknown coherent light source, active spectral measurement can be realized. Each time the fiber FP filter filters out one tooth of the chip optical comb and performs beat frequency with the incident signal, the beat frequency signal within the bandwidth of the short-pass filter can be detected, and then high-precision unknown signal spectral measurement within the entire spectral range is realized through scanning and single-sideband frequency shifting.

[0022] (3) The microcavity optical comb can be locked to an absolute frequency and has extremely high spectral stability. The use of the fiber FP filter can fiberize and integrate the entire system. There is no need to apply mechanical scanning components, and its signal processing is simple and high-speed detection can be realized. It is more easily applied to mobile loads such as cars and airplanes and has stronger stability.

[0023] (4) Due to its characteristics of high speed, large dynamic range, and high spectral resolution, this technology can improve the accuracy and speed of gas spectral detection to a certain extent in the fields of atmospheric remote sensing, combustion diagnosis, industrial gas emissions, and greenhouse gas detection, adding ways for the practical application and deployment of the optical frequency comb spectroscopy system. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the optical path of the measurement system;

[0025] Figure 2 It is a schematic diagram of the principle of the FP interferometer;

[0026] Figure 3 It is a schematic diagram of the change of the center wavelength of the passband of the fiber optic FP filter with voltage;

[0027] Figure 4 It is the oscilloscope sampling curve obtained by a single scan.

[0028] 1. Light source; 2. IQ electro-optic modulator; 3. Fiber optic FP filter; 4. Piezoelectric drive controller; 5. Optical switch; 6. Gas cell to be measured; 7. Light source to be measured; 8. First fiber optic coupler; 9. Low-pass filter; 10. Second fiber optic coupler; 11. Photoelectric detector. Detailed Embodiments

[0029] The technical solutions of the present invention will be further described below with reference to the drawings and embodiments.

[0030] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0031] Embodiment 1

[0032] As Figure 1 shown, a frequency-shifted filtering spectroscopy measurement system based on a modulated microcavity optical frequency comb includes a light source 1, an IQ electro-optic modulator 2, a fiber optic FP filter 3, a piezoelectric drive controller 4, an optical switch 5, a gas cell 6 to be measured using the active spectrometer function, a light source 7 to be measured using the passive function, a first fiber optic coupler 8, a low-pass filter 9, a second fiber optic coupler 10, and a photoelectric detector 11.

[0033] A chip-integrated microcavity optical frequency comb with a known repetition frequency and offset frequency is used as the emission light source 1. The electro-optic modulation effect of the IQ electro-optic modulator 2 is utilized to suppress its carrier and one sideband so that a single-sideband signal is output. After passing through gas absorption, it is coupled into the fiber optic FP cavity filter 3 using polarization-maintaining single-mode fiber, and a specific scanning signal drive voltage is applied to the fiber optic FP cavity filter 3 through the piezoelectric drive controller 4.

[0034] The light filtered by the FP cavity passes through an optical switch and a gas cell to be measured. The component at the corresponding absorption line is absorbed, and the signal after absorption attenuation is received by a photodetector.

[0035] Or the light filtered by the FP cavity and the light to be measured are combined by a first fiber coupler to generate a beat frequency. The signal less than half of the repetition frequency is filtered out by a low-pass filter, and the spectral signal is received by a photodetector, and the spectrum of the signal to be measured is obtained by inversion.

[0036] The filtered optical signal is detected by a photodetector 11 and the waveform is displayed on an oscilloscope. This waveform corresponds to the intensity of the transmitted optical signal at each wavelength when the cavity length is scanned. By stepwise adjusting the modulation frequency of the IQ electro-optic modulator 2, the wavelength of the single sideband can be scanned to cover the spectral range of the light source 1 emitted by the chip-integrated microcavity optical comb, effectively realizing the measurement of high-resolution absorption spectra.

[0037] The cavity length can be scanned by changing the driving voltage applied to the piezoelectric driving controller 4 , thereby scanning the transmitted wavelength. As Figure 3 shown, during the process of the driving voltage changing from 4V to 14V, the central wavelength of the transmitted light gradually changes from 1580nm to 1506nm, and the scanning frequency can reach up to 800Hz. By selecting appropriate bias voltage and scanning voltage magnitude, high-speed detection of the signal in the band to be measured can be achieved.

[0038] A frequency-shifted filtering spectral measurement method based on a modulated microcavity optical comb, including

[0039] Using a continuous-wave laser with a wavelength of 1550nm to pump a microring cavity to obtain the light source 1 emitted by the chip-integrated microcavity optical comb. The frequency intervals of the light source 1 are equal and about 20GHz. The signal processing process between the chip-integrated microcavity optical frequency comb of the light source and the IQ electro-optic modulator 2: The light source is used as the signal to be measured for demonstration. After being coupled and output through a tapered fiber, the light source is input into the IQ electro-optic modulator 2 through a flange.

[0040] The IQ electro-optic modulator 2 applies a modulation signal through an arbitrary signal generator to generate a single sideband output signal with carrier sideband suppression, and the signals at each central wavelength are sequentially filtered out through the FP cavity scanning of the fiber FP filter 3 and enter the optical switch 5. Then there are two test optical paths, and one of them is selected according to needs:

[0041] The first test optical path: When the optical switch is placed in channel a, this spectrometer is used to detect the absorption spectrum of the gas sample to be measured; the light filtered by the FP cavity passes through the optical switch and the gas cell to be measured. The component at the corresponding absorption line is absorbed, and the signal after absorption attenuation is received by a photodetector.

[0042] Second test optical path: When the optical switch is placed in channel b, the spectrometer is used to detect the spectrum of the unknown signal. The light filtered by the FP cavity and the light to be measured are combined by the first fiber optic coupler to generate a beat frequency. The signal less than half of the repetition frequency is filtered out by the low-pass filter, and the spectrum signal is received by the photodetector, and the spectrum of the signal to be measured is obtained by inversion.

[0043] The second fiber optic coupler is only used to combine the two channels and share a single photodetector. Only the first test optical path or the second test optical path works in a single test.

[0044] Whenever the FP cavity scans a complete cycle, the modulation frequency of the signal source is increased by one step. In this way, when the modulation frequency increases from 0 to 20 GHz in steps of 50 MHz, the spectrum signals within the effective spectral width of the entire microcavity optical comb can be measured. After setting the modulation frequency of the signal source and the scanning parameters of the driving voltage of the FP cavity, Figure 4 the oscilloscope sampling curve shown in the figure is obtained. The abscissa is the voltage of the photoelectric signal proportional to the light intensity, and the ordinate is the scanning time proportional to the frequency. The overall curve presents an equally spaced comb-like shape. The linewidth of the fiber FP cavity limits the linewidth of a single comb tooth and the resolution of the entire system. It can be seen from the results that within a detection time of about 0.1 s, the transmission wavelength of the single fiber FP cavity can sequentially scan the signal to be measured and obtain the output signal. Subsequently, the spectrum of the incident signal can be further inverted by calibrating the wavelength and intensity.

[0045] The resolution of the present invention is mainly limited by the linewidth of the FP cavity and the modulation frequency step. By comprehensively considering the resolution and acquisition time to design the system parameters, high-resolution and high-speed spectral acquisition can be fully realized.

[0046] Therefore, the present invention adopts the above-mentioned method and system for measuring shifted-frequency filtered spectrum based on modulated microcavity optical comb, which can avoid the disadvantage that the resolution of the current spectral detection system is reduced due to limited mechanical scanning rate or fringe deterioration at the signal receiving end, making it impossible to achieve high-resolution and fast spectral detection with this system. The high-resolution spectral detection technology developed based on this method is a potentially ideal tool for multi-component, large-range, continuous and real-time monitoring. This tool mainly based on spectroscopic methods is conducive to establishing a regional gas monitoring system. By matching the system designed with this method, the advantages of miniaturization and high spectral resolution of the chip optical comb can be utilized, and it can be applied to gas monitoring and open atmosphere gas monitoring, and is expected to be widely used in environmental protection, climate, industrial safety and other fields.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A frequency-shifted filtering spectral measurement system based on a modulated microcavity optical frequency comb, characterized in that It includes a light source, an IQ electro-optic modulator, an optical fiber FP filter, a piezoelectric drive controller, an optical switch, a first test optical path and a second test optical path, a second optical fiber coupler, and a photodetector in sequence; The first test optical path includes a gas pool to be tested, and two ends of the gas pool to be tested are respectively connected to an optical switch and a photoelectric detector; The second test optical path includes a light source to be tested, a first optical fiber coupler, and a low-pass filter; the light source to be tested is connected to the first optical fiber coupler, two ends of the first optical fiber coupler are respectively connected to an optical switch and a low-pass filter, and the low-pass filter is connected to the second optical fiber coupler; The chip-integrated microcavity optical frequency comb is used to emit a light beam, which passes through an IQ electro-optical modulator to generate a single-sideband output signal with carrier sideband suppression. The single-sideband output signal passes through an optical fiber FP filter to filter out the signals at each center wavelength in turn and enter the optical switch. When the optical switch is placed in the first test optical path, it is used to detect the absorption spectrum of the gas sample to be tested: the light filtered by the FP cavity passes through the optical switch and the gas pool to be tested, the component at the corresponding absorption line is absorbed, and the photodetector receives the signal after absorption attenuation; When the optical switch is placed in the second test optical path, it is used to detect the unknown signal spectrum: the light filtered by the FP cavity and the light to be tested are combined under the action of the first fiber coupler to generate a beat frequency, and the signal less than half of the repetition frequency is filtered out by the low-pass filter. The spectrum signal is received by the photodetector, and the spectrum of the signal to be tested is inverted to obtain the spectrum of the signal to be tested; The second optical fiber coupler combines the first test optical path and the second test optical path, and they share a photoelectric detector. In a single test, only the first test optical path or the second test optical path is effective. The light beam emitted by the light source to be measured enters the first optical fiber coupler and is combined with the signals at each central wavelength. The combined signal low-pass filter is used to suppress high-frequency noise and interference signals. The photodetector receives the combined light beam.

2. The frequency-shifted filtering spectral measurement system based on a modulated microcavity optical comb according to claim 1, wherein An FP cavity is provided in the optical fiber FP filter, and the modulation frequency of the signal source is increased by one step after the FP cavity scans one cycle.

3. The frequency-shifted filtering spectral measurement system based on a modulated microcavity optical comb according to claim 1, wherein The light source, the IQ electro-optic modulator, the optical fiber FP filter, the piezoelectric drive controller, the optical switch, the first test optical path or the second test optical path, the second optical fiber coupler, and the photoelectric detector are sequentially connected by optical fibers.

4. A frequency-shifted filtering spectral measurement system based on a modulated microcavity optical frequency comb according to claim 1, characterized in that, Add an amplifier between the optical fiber FP filter and the optical switch; Or an amplifier is added between the light source and the IQ electro-optic modulator.

5. A frequency shift filtering spectral measurement method based on a modulated microcavity optical frequency comb, characterized in that, The chip-integrated microcavity optical frequency comb is used to emit a light beam, which passes through an IQ electro-optical modulator to generate a single-sideband output signal with carrier sideband suppression. The single-sideband output signal passes through an optical fiber FP filter to filter out the signals at each center wavelength in turn and enter the optical switch. When the optical switch is placed in the first test optical path, it is used to detect the absorption spectrum of the gas sample to be tested: the light filtered by the FP cavity passes through the optical switch and the gas pool to be tested, the component at the corresponding absorption line is absorbed, and the photodetector receives the signal after absorption attenuation; When the optical switch is placed in the second test optical path, it is used to detect the unknown signal spectrum: the light filtered by the FP cavity and the light to be tested are combined under the action of the first fiber coupler to generate a beat frequency, and the signal less than half of the repetition frequency is filtered out by the low-pass filter. The spectrum signal is received by the photodetector, and the spectrum of the signal to be tested is inverted to obtain the spectrum of the signal to be tested; The second optical fiber coupler combines the first test optical path and the second test optical path, sharing a single photodetector. Only the first test optical path or the second test optical path functions during a single test. The light beam emitted by the light source to be measured enters the first optical fiber coupler and is combined with the signals at each center wavelength. The combined signal low-pass filter is used to suppress high-frequency noise and interference signals. The photodetector receives the combined light beam.

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