Frequency shift filtering spectral measurement method and system based on modulation microcavity optical comb

Abstract

The invention provides a frequency shift filtering spectrum measurement method and system based on a modulation microcavity optical comb, and belongs to the field of spectrum precision measurement, and the system comprises a chip integrated microcavity optical frequency comb of a light source, an electro-optical modulator, an optical fiber FP filter, a piezoelectric driving controller, an optical switch, a first test light path or a second test light path, a second optical fiber coupler, and a photoelectric detector. According to the frequency shift filtering spectral measurement method and system based on the modulated microcavity optical comb, the advantages of miniaturization and high spectral resolution of the chip optical comb can be played, and the method and system are used for gas monitoring and open atmosphere gas monitoring and are expected to be widely applied to the fields of environmental protection, climate, industrial safety and the like.

Description

Technical Field

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

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

[0003] The electro-optic modulator can generate sidebands on both sides of the input carrier. The frequency difference relative to the carrier is the modulation frequency. The IQ modulator based on the dual parallel Mach-Zehnder modulator can suppress the carrier and a certain sideband. By reasonably setting the working point and bias voltage of the modulator, the dynamic tuning of the single sideband can be achieved by changing only 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 comb teeth of the original microcavity optical comb). At this time, the modulation frequency can be stepped and scanned across the entire comb tooth interval to achieve the coverage of the single sideband in the entire spectral range. The fiber FP filter is a resonant cavity made based on the principle of multi-beam interference. 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 a narrowband transmission peak in the spectrum. By changing the voltage applied to the piezoelectric ceramic, the cavity length can be tuned to control the central wavelength of the transmission peak.

[0004] The classic FP resonant cavity consists of two plates with high reflectivity thin film surfaces, such as Figure 2 As shown, L is the driving voltage on the piezoelectric drive controller that can scan the cavity, θ is the incident angle of the light, which is 0 in the fiber FP cavity. For details, please refer to "Optics" compiled by You Pu and Yu Guoping in July 2003 and published in July 2003. Summary of the invention

[0005] The purpose of the present invention is to provide a frequency-shift filtering spectrum measurement method and system based on a modulated microcavity optical comb. The comb teeth of the input microcavity optical comb signal and the intensity of the sidebands it generates are modulated by an IQ electro-optical modulator to suppress the carrier and another sideband. A photodetector is then used to measure the signal after high-speed scanning optical fiber FP cavity filtering. In this way, by changing the modulation frequency, the generated single-sideband comb teeth are scanned across the entire spectral range of the microcavity optical comb, and a spectral resolution at the level of the comb tooth line width can be obtained.

[0006] To achieve the above-mentioned purpose, the present invention provides a frequency-shift filtering spectrum measurement system based on a modulated microcavity optical comb, which comprises a light source, an IQ electro-optical 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 optical fiber coupler, and a photodetector.

[0007] Preferably, 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.

[0008] Preferably, 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 coupler.

[0009] Preferably, 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.

[0010] Preferably, 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 photodetector are sequentially connected by optical fibers.

[0011] Preferably, an amplifier may be added between the optical fiber FP filter and the optical switch; Alternatively, an amplifier may be added between the light source and the IQ electro-optic modulator.

[0012] Preferably, the light source is emitted by a chip-integrated microcavity optical frequency comb.

[0013] A frequency-shift filtering spectrum measurement method based on modulated microcavity optical comb, using a chip-integrated microcavity optical frequency comb to emit a light beam, the light beam passes through an IQ electro-optical modulator to generate a single-sideband output signal with carrier sideband suppression, and 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 an 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 shares a photoelectric detector. Only the first test optical path or the second test optical path works in a single test. The light beam emitted by the light source to be tested 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 photoelectric detector receives the combined light beam.

[0014] Therefore, the present invention adopts the above-mentioned frequency-shift filtering spectrum measurement method and system based on modulated microcavity optical comb, and the technical effects are as follows: (1) The light beam emitted by the chip optical comb light source is modulated by an IQ electro-optical modulator, and the single-sideband output is received by the optical fiber FP filter in conjunction with the photoelectric detection system to receive the narrow linewidth signal within the transmission passband. The signal size of the detector under the corresponding voltage can be directly read out, and then the modulation frequency is step-adjusted to obtain the spectral information within the entire chip optical comb spectrum width in a single-sideband frequency shifting manner, which can realize rapid absorption spectrum measurement.

[0015] (2) The teeth of the chip optical comb have strong coherence, and active spectral measurement can be achieved for unknown coherent light sources. The fiber FP filter filters out one tooth of the chip optical comb each time to beat with the incident signal. The beat signal within the bandwidth of the short-pass filter can be detected, and then high-precision unknown signal spectral measurement in the entire spectral range can be achieved through scanning and single-sideband frequency shifting.

[0016] (3) The microcavity optical comb can be locked to an absolute frequency and has extremely high spectral stability. The use of fiber FP filters can make the entire system fiber-optic and integrated, without the need for mechanical scanning components. Its signal processing is simple and can achieve high-speed detection. It is easier to apply to mobile loads such as automobiles and aircraft, and has stronger stability.

[0017] (4) Due to its fast speed, large dynamic range and high spectral resolution, this technology can improve the accuracy and speed of gas spectral detection in the fields of atmospheric remote sensing, combustion diagnosis, industrial gas emissions and greenhouse gas detection to a certain extent, adding a way for the practical application and deployment of optical comb spectroscopy systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the optical path of the measurement system; Figure 2 This is the schematic diagram of the FP interferometer; Figure 3 This is a schematic diagram of the variation of the passband center wavelength of the optical fiber FP filter with voltage; Figure 4 Obtain an oscilloscope sampling trace for a single sweep.

[0019] 1. Light source; 2. IQ electro-optic modulator; 3. Optical fiber FP filter; 4. Piezoelectric drive controller; 5. Optical switch; 6. Gas pool to be measured; 7. Light source to be measured; 8. First optical fiber coupler; 9. Low-pass filter; 10. Second optical fiber coupler; 11. Photodetector. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0021] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs. Example

[0022] like Figure 1 As shown, a frequency-shift filtering spectroscopy measurement system based on a modulated microcavity optical comb includes a light source 1, an IQ electro-optical modulator 2, an optical fiber FP filter 3, a piezoelectric drive controller 4, an optical switch 5, a gas pool to be measured using an active spectrometer function 6, a light source to be measured using a passive function 7, a first optical fiber coupler 8, a low-pass filter 9, a second optical fiber coupler 10, and a photodetector 11.

[0023] A chip-integrated microcavity optical comb with known repetition frequency and bias frequency is used as the emitting light source 1, and the electro-optic modulation effect of the IQ electro-optic modulator 2 is utilized to suppress its carrier and one sideband so as to output a single sideband signal, which is then coupled into the optical fiber FP cavity filter 3 using a polarization-maintaining single-mode optical fiber after gas absorption, and a driving voltage of a specific scanning signal is applied to the optical fiber FP cavity filter 3 through a piezoelectric drive controller 4.

[0024] The light after the optical fiber FP cavity filter 3 passes through the optical switch and the gas pool to be measured, and the component at the corresponding absorption line is absorbed, and the photoelectric detector 11 receives the signal after absorption attenuation.

[0025] Or the light after the optical fiber FP cavity filter 3 and the light to be measured are combined under the action of the first optical fiber coupler 8 to generate a beat frequency, and a signal less than half of the repetition frequency is filtered out by a low-pass filter 9, and the spectrum signal is received by the photoelectric detector 11, and the spectrum of the signal to be measured is inverted.

[0026] The filtered light signal is detected by the photodetector 11 and a waveform is displayed on the oscilloscope. The waveform corresponds to the intensity of the transmitted light signal at each wavelength when the cavity length is scanned. By stepping through the modulation frequency of the IQ electro-optic modulator 2, the wavelength of the single sideband can scan and cover the spectral range of the light source 1 emitted by the entire chip-integrated microcavity optical comb, thereby effectively realizing the measurement of high-resolution absorption spectra.

[0027] The cavity length can be scanned by changing the drive voltage applied to the piezoelectric drive controller 4. , thereby scanning the transmission wavelength, such as Figure 3 As shown in the figure, when the driving voltage changes 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 the appropriate bias voltage and scanning voltage, high-speed detection of the signal in the band to be measured can be achieved.

[0028] A frequency-shift filtering spectrum measurement method based on a modulated microcavity optical comb, comprising: The chip-integrated microcavity optical comb is pumped by a continuous wave laser with a wavelength of 1550nm to obtain the light source 1 emitted by the chip-integrated microcavity optical comb. The frequency interval of the light source 1 is equal and the size is about 20GHz. The signal processing process between the chip-integrated microcavity optical frequency comb of the light source 1 and the IQ electro-optical modulator 2: the light source 1 is used as the signal to be tested for demonstration. The light source 1 outputted by the tapered fiber coupling is input into the IQ electro-optical modulator 2 through the flange.

[0029] The IQ electro-optic modulator 2 generates a single-sideband output signal with carrier sideband suppression by applying a modulation signal through an arbitrary signal generator, and filters out the signals at each center wavelength in turn through the FP cavity scanning of the optical fiber FP filter 3 and enters the optical switch 5. After that, there will be two test optical paths, and one of them can be selected according to the needs: First test optical path: When the optical switch is placed in channel a, the spectrometer is used to detect the absorption spectrum of the gas sample to be tested; the light after the optical fiber FP cavity filter 3 passes through the optical switch 5 and the gas pool to be tested 6, the component at the corresponding absorption line is absorbed, and the photodetector 11 receives the signal after absorption attenuation.

[0030] Second test optical path: When the optical switch 5 is placed in channel b, the spectrometer is used to detect the unknown signal spectrum. The light after the optical fiber FP cavity filter 3 and the light to be measured are combined under the action of the first optical fiber coupler 8 to generate a beat frequency, and the signal less than half of the repetition frequency is filtered out by the low-pass filter 9. The spectrum signal is received by the photodetector 11, and the spectrum of the signal to be measured is inverted to obtain.

[0031] The second optical fiber coupler 10 is only used to combine the two channels to share a photoelectric detector 11, and only the first test optical path or the second test optical path is effective in a single test.

[0032] Each time the FP cavity scans a 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 spectral signal within the effective spectrum 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 FP cavity driving voltage, we get Figure 4 The oscilloscope sampling curve shown in the figure shows that the voltage of the photoelectric signal is proportional to the light intensity on the horizontal axis and the scanning time is proportional to the frequency on the vertical axis. The overall curve is an equally spaced comb-shaped curve. The line width of the fiber FP cavity limits the line width of a single comb tooth and the resolution of the entire system. From the results, it can be seen that within a detection time of about 0.1s, the transmission wavelength of the single fiber FP cavity can be scanned sequentially across the signal to be measured and the output signal can be obtained. The spectrum of the incident signal can be further inverted by calibrating the wavelength and intensity.

[0033] The resolution of the present invention is mainly limited by the FP cavity line width and the modulation frequency step. By comprehensively considering the resolution and acquisition time to design the system parameters, high-resolution and high-speed spectrum acquisition can be fully achieved.

[0034] Therefore, the present invention adopts the above-mentioned frequency-shift filtering spectral measurement method and system based on modulated microcavity optical comb, which can avoid the disadvantage that the resolution of the current spectral detection system is reduced due to mechanical scanning rate limitation or stripe degradation at the signal receiving end, making it impossible to use the system to achieve high-resolution rapid spectral detection. The high-resolution spectral detection technology developed based on this method is a potential ideal tool for multi-component, large-scale, continuous real-time monitoring. This tool, which uses spectroscopy as the main means, is conducive to the establishment of a regional gas monitoring system. By matching the system designed by this method, the advantages of the miniaturization and high spectral resolution of the chip optical comb can be brought into play, and gas monitoring and open atmospheric gas monitoring can be utilized, which is expected to be widely used in environmental protection, climate, industrial safety and other fields.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A frequency-shift filtering spectrum measurement system based on a modulated microcavity optical comb, characterized in that: The system comprises in sequence 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 or a second test optical path, a second optical fiber coupler, and a photoelectric detector.

2. A frequency-shift filtering spectrum measurement system based on a modulated microcavity optical comb according to claim 1, characterized in that: 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.

3. The frequency-shift filtering spectrum measurement system based on modulated microcavity optical comb according to claim 1, characterized in that: 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 coupler.

4. The frequency-shift filtering spectrum measurement system based on modulated microcavity optical comb according to claim 1, characterized in that: 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.

5. The frequency-shift filtering spectrum measurement system based on modulated microcavity optical comb according to claim 1, characterized in that: 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.

6. The frequency-shift filtering spectrum measurement system based on modulated microcavity optical comb according to claim 1, characterized in that: An amplifier can be added between the optical fiber FP filter and the optical switch; Alternatively, an amplifier may be added between the light source and the IQ electro-optic modulator.

7. The frequency-shift filtering spectrum measurement system based on modulated microcavity optical comb according to claim 1, characterized in that: The light source is emitted through a chip-integrated microcavity optical frequency comb.

8. A method for frequency shift filtering spectrum measurement system based on modulated microcavity optical comb according to any one of claims 1 to 7, 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, 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.

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