Spectrum analyzer

Abstract

The utility model discloses a spectrum analyzer, comprising a tunable laser used for outputting frequency laser; the frequency expansion module is used for receiving the frequency laser output by the tunable laser, performing frequency expansion processing and then outputting frequency expansion laser; the signal acquisition module is used for acquiring a signal after the frequency expansion laser output by the frequency expansion module passes through the object to be measured; and the data processing module is used for analyzing the signal acquired by the signal acquisition module to obtain the frequency response of the to-be-detected object. According to the spectrum analyzer disclosed by the utility model, the frequency laser output by the tunable laser is subjected to frequency conversion through the frequency expansion module, so that the bandwidth of the spectrum analyzer is greatly expanded, and full-wave band spectrum analysis from purple light to infrared light is realized.

Description

Technical Field

[0001] The utility model belongs to the technical field of spectrum analysis and measurement, and in particular relates to a spectrum analyzer. Background Art

[0002] The most important indicators of a spectrum analyzer are its resolution and test bandwidth. Resolution determines how fine a spectral structure can be tested. High spectral resolution is essential for analyzing the chemical composition of materials, air pollution, and biological pathology research. Commercial spectrometers are usually based on gratings, prisms, and other spectroscopic devices, and their resolution is often only tens of GHz. High-resolution spectral measurement can be achieved using continuously tunable lasers.

[0003] A continuously tunable laser can output a narrow linewidth laser whose frequency changes continuously over time. After the laser passes through the passive device to be measured, it is received by a photodetector. Since the laser frequency is tuned over time, the frequency response of the device is converted into a signal output that changes over time. Therefore, by analyzing the signal, the absorption spectrum or reflection spectrum of the device can be measured. Similarly, the beat frequency of the laser and the optical signal to be measured will also generate a radio frequency signal that changes over time, which reflects the frequency component of the optical signal to be measured. The resolution of this method is only related to the laser, and the resolution can reach the order of 100kHz.

[0004] The bandwidth of the spectrometer determines the frequency range of the spectral measurement. A large bandwidth can measure the dispersion of an object, complex gas composition, or the fluorescence spectrum of biological materials. However, existing broadband tunable lasers can only be achieved in the near-infrared band, and the bandwidth of spectral analysis technology based on continuously tunable lasers is also limited to the near-infrared band.

[0005] The utility model utilizes optical nonlinear effect to perform frequency conversion, greatly expands the bandwidth of the spectrum analyzer, and realizes spectrum analysis from ultraviolet light to infrared light. Utility Model Content

[0006] The utility model aims to provide a spectrum analyzer to solve the defect of narrow spectrum frequency measurement range of the spectrum analyzer in the prior art.

[0007] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0008] A spectrum analyzer, comprising:

[0009] Tunable laser for outputting frequency laser;

[0010] A frequency extension module, used for receiving the frequency laser output by the tunable laser, performing frequency extension processing, and then outputting the frequency extended laser;

[0011] A signal acquisition module, used to acquire the signal after the frequency extension laser output by the frequency extension module passes through the object to be measured;

[0012] The data processing module is used to analyze the signal collected by the signal collection module to obtain the frequency response of the object to be measured.

[0013] In the utility model, the frequency extension module includes one or more of a frequency multiplication module and a sum / difference frequency module.

[0014] In some implementation schemes of the present invention, the frequency doubling module includes a first optical amplifier and a first frequency conversion device.

[0015] Furthermore, the first frequency conversion device is composed of a nonlinear crystal or a waveguide.

[0016] Preferably, the nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

[0017] In some embodiments of the present invention, the sum / difference frequency module includes a pump laser, a second optical amplifier, a third optical amplifier and a second frequency conversion device.

[0018] Furthermore, the second frequency conversion device is composed of a nonlinear crystal or a waveguide.

[0019] Preferably, the nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

[0020] In the utility model, the signal acquisition module includes a photoelectric detector and also includes an oscilloscope or an acquisition card.

[0021] In the utility model, the data processing module includes a data processing device, and the data processing device includes a computer.

[0022] The utility model can be improved as follows: the spectrum analyzer further comprises a frequency calibration module, which is used to receive the frequency laser output by the tunable laser for calibration and measure the frequency output by the tunable laser.

[0023] Furthermore, the frequency calibration module includes a frequency calibration device, and the frequency calibration device includes one of a fiber ring cavity, a fiber unequal-arm interferometer, and an optical frequency comb.

[0024] The utility model has the following beneficial effects:

[0025] (1) The spectrum analyzer of the utility model converts the frequency of the laser output by the tunable laser through the frequency extension module, which greatly expands the bandwidth of the spectrum analyzer and realizes full-band spectrum analysis from ultraviolet light to infrared.

[0026] (2) The frequency calibration module of the spectrum analyzer of the utility model calibrates the frequency of the laser before the frequency conversion is performed, and the converted frequency is also calibrated at the same time, so as to obtain the laser frequency after the frequency conversion for spectrum analysis with higher frequency accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The technical solution of the utility model is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0028] Figure 1 This is a schematic diagram of the overall structure of the spectrum analyzer of Embodiment 1 of the utility model;

[0029] Figure 2 This is a schematic diagram of the overall structure of the spectrum analyzer of Embodiment 2 of the utility model;

[0030] Figure 3 This is a physical picture of the spectrum analyzer of Example 1 of the utility model;

[0031] Figure 4 This is the wavelength of the frequency-doubled light generated by Example 1 of the utility model;

[0032] Figure 5 This is the transmission spectrum of the optical fiber ring cavity of the frequency calibration module of Example 1 of the utility model;

[0033] Figure 6 This is a diagram of the free spectrum range of the optical fiber ring cavity in Example 1 of the utility model;

[0034] Figure 7 It is the wavelength diagram of the laser of Example 1 of the utility model;

[0035] Figure 8 is the frequency sweep speed of the laser in Example 1 of the utility model;

[0036] Fig. 9 It is a through-color spectrum of silicon nitride;

[0037] Fig.10 is the integrated dispersion diagram of the silicon nitride microcavity;

[0038] The markings in the figure are as follows: 1. tunable laser; 2. frequency extension module; 3. signal acquisition module; 4. data processing module; 5. frequency calibration module; 6. object to be measured; 7. photodetector; 8. oscilloscope; 9. fiber ring cavity; 201. frequency doubling module; 202. sum / difference frequency module; 2011. first optical amplifier; 2012. first frequency conversion device; 2021. pump laser; 2022. second optical amplifier; 2023. second frequency conversion device; 2024. third optical amplifier. DETAILED DESCRIPTION

[0039] The utility model provides a spectrum analyzer, which uses optical nonlinear effects to convert frequencies, and uses broadband phase matching nonlinear crystals to convert broadband continuously tunable lasers in the near-infrared band to visible light, mid-infrared and mid-infrared bands. At the same time, by calibrating the frequency of the laser in the near-infrared where optical devices are mature, the frequency of the converted laser is calibrated, and the calibration can improve the frequency accuracy of spectrum analysis. The details are as follows:

[0040] A spectrum analyzer, comprising:

[0041] A tunable laser 1, used for outputting frequency laser;

[0042] The frequency extension module 2 is used to receive the frequency laser output by the tunable laser 1, perform frequency extension processing, and then output the frequency extended laser;

[0043] A signal acquisition module 3, used for acquiring the signal after the frequency expansion laser output by the frequency expansion module 2 passes through the object to be measured 6;

[0044] The data processing module 4 is used to analyze the signal collected by the signal collection module 3 to obtain the frequency response of the object to be measured 6.

[0045] In the present invention, the frequency extension module 2 includes one or more of a frequency multiplication module 201 and a sum / difference frequency module 202 .

[0046] Frequency doubling is a nonlinear optical process in which two photons with the same frequency interact with nonlinear materials and can combine to produce a new photon with twice the energy of the initial photon (doubled frequency) while maintaining coherence. The realization of this frequency conversion relies on nonlinear materials. Nonlinear crystals such as BBO and LBO and periodic polarization nonlinear crystals or waveguides such as PPLN and PPKDP can all achieve this function. Other nonlinear materials can also be used. Nonlinear crystals such as BBO and LBO achieve phase matching by adjusting the angle at which light is incident on the crystal. By focusing with a lens, multiple angles can be incident simultaneously, thereby increasing the phase matching bandwidth. Periodic polarization nonlinear crystals or waveguides such as PPLN and PPKDP achieve phase matching by changing the polarization period. Broadband phase matching can be achieved by cascading different polarization periods. In some embodiments of the utility model, the frequency doubling module 201 includes a first optical amplifier 2011 and a first frequency conversion device 2012.

[0047] Furthermore, the first frequency conversion device 2012 is composed of a nonlinear crystal or a waveguide.

[0048] Preferably, the nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

[0049] Sum frequency and difference frequency are similar to frequency doubling, and are also nonlinear optical processes, in which two photons with frequencies f1 and f2 (f1>f2) can be combined to produce high-frequency photons with a frequency of f3=f1+f2, which is sum frequency. The generation of photons with f3=f1-f2 is a difference frequency process. Broadband phase matching can be achieved by selecting nonlinear materials, designing the crystal incident angle, or designing the polarization period of periodically polarized crystals. Two photons with the same frequency interact with nonlinear materials and can combine to produce a new photon with twice the energy of the initial photon (double the frequency and halve the wavelength) while maintaining coherence. The realization of this frequency conversion depends on nonlinear materials. Nonlinear crystals such as BBO and LBO and periodically polarized nonlinear crystals or waveguides such as PPLN and PPKDP can achieve this function.

[0050] In some implementation schemes of the present invention, the sum / difference frequency module 202 includes a pump laser 2021 , a second optical amplifier 2022 , a third optical amplifier 2024 and a second frequency conversion device 2023 .

[0051] Furthermore, the second frequency conversion device 2023 is composed of a nonlinear crystal or a waveguide.

[0052] Preferably, the nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

[0053] The pump laser 2021 has a fixed frequency, and its frequency can be locked to a frequency reference, or a wavelength meter can be used to accurately measure the frequency. The measured frequency is fp, and by calibrating f, the converted optical frequency can be calculated in combination with fp.

[0054] In the present invention, the signal acquisition module 3 includes a photoelectric detector 7 and also includes an oscilloscope 8 or an acquisition card.

[0055] In the present invention, the data processing module 4 includes a data processing device, and the data processing device includes a computer. The collected signal is analyzed by the data processing device, and the data processing device includes a computer and an algorithm, and can also be implemented by a field programmable gate array (FPGA). The frequency information output by the frequency calibration device can be used to calibrate the instantaneous frequency of the laser at different times, thereby solving the frequency response of the object to be measured 6.

[0056] The present invention can be improved as follows: the spectrum analyzer further comprises a frequency calibration module 5 for receiving the frequency laser output by the tunable laser 1 for calibration and measuring the frequency output by the tunable laser 1 .

[0057] Furthermore, the frequency calibration module 5 includes a frequency calibration device, and the frequency calibration device includes one of a fiber ring cavity 9, a fiber unequal-arm interferometer, and an optical frequency comb.

[0058] The transmission signal of the fiber ring cavity 9 or the fiber unequal-arm interferometer has a periodic frequency characteristic, so it can be used as a frequency reference after calibration. The frequency components of the optical frequency comb are equally spaced, so by measuring the beat frequency of the tunable laser 1 and the optical frequency comb, the frequency of the laser output can also be measured. The output frequency of the laser at different times can be obtained using a frequency calibration device. It is used for correction in subsequent data processing equipment. The output signal of the frequency calibration device is also received by the signal acquisition device.

[0059] Example 1

[0060] like Figure 1 The optical spectrum analyzer shown comprises:

[0061] A tunable laser 1, used for outputting frequency laser;

[0062] The frequency extension module 2 is used to receive the frequency laser output by the tunable laser 1, perform frequency extension processing, and then output the frequency extended laser; the frequency extension module 2 is a frequency doubling module 201;

[0063] A signal acquisition module 3, used for acquiring the signal after the frequency expansion laser output by the frequency expansion module 2 passes through the object to be measured 6;

[0064] The data processing module 4 is used to analyze the signal collected by the signal collection module 3 to obtain the frequency response of the object to be measured 6;

[0065] The frequency calibration module 5 is used to receive the frequency laser output by the tunable laser 1 for calibration and measure the frequency output by the laser.

[0066] Specifically, the present invention realizes through experiments that near-infrared lasers are extended to the red light band by frequency doubling to perform spectral analysis. Figure 3 The spectrum analyzer shown uses a continuously tunable laser 1 with a wavelength of 1530-1590nm. The output laser is divided into two paths. One path is amplified by an erbium-doped fiber amplifier and then undergoes broadband frequency conversion by a PPLN periodically polarized lithium niobate waveguide. The polarization period of the PPLN is designed to be continuously variable from 18.1 to 19.9 microns. The frequency-doubled light generated has a range of 765-795nm, such as Figure 4 As shown, the light is then directed toward the object 6 to be measured.

[0067] The other laser generated by the tunable laser 1 is frequency calibrated through the frequency calibration device fiber ring cavity 9, and the transmission spectrum of the fiber ring cavity 9 is collected by the signal acquisition module 3 composed of a photodetector 7 and an oscilloscope 8, such as Figure 5 The spacing of the absorption peaks in its transmission spectrum (free spectral range) has been accurately calibrated, as shown in Figure 6 As shown. Therefore, the wavelength of the laser at different times can be calculated by a data processing device composed of a computer and an algorithm, such as Figure 7 As shown. However, due to the laser sweep speed jitter (such as Figure 8 The relative frequency accuracy of the test can reach 10 -6 .

[0068] The broadband tunable red light generated is used for integrated optical chip testing, and the integrated silicon nitride microcavity is taken as an example here. When the laser is swept, the chip output signal that changes with time is collected by the signal acquisition module 3 composed of the photodetector 7 and the oscilloscope 8. The signal is input to the data processing module 4 for processing. By combining the frequency calibration equipment, the output wavelength λ(t) of the laser can be obtained. Due to the energy conservation in the frequency doubling process, it can be known that the wavelength of the red light is 2λ(t). Therefore, the time of the chip output signal can be converted into wavelength or frequency to obtain the frequency response of the chip, such as Fig. 9 As shown, the intrinsic line width of the absorption peak of the chip is 63.6MHz, and the absorption peak of this scale cannot be measured by a grating spectrometer. By measuring the absorption peak spacing of the chip through broadband, the integrated dispersion of the chip can be obtained as follows: Fig.10 shown.

[0069] Example 2

[0070] like Figure 2 The optical spectrum analyzer shown comprises:

[0071] A tunable laser 1, used for outputting frequency laser;

[0072] The frequency extension module 2 is used to receive the frequency laser output by the tunable laser 1, perform frequency extension processing, and then output the frequency extended laser; the frequency extension module 2 is a sum / difference frequency module 202;

[0073] A signal acquisition module 3, used for acquiring the signal after the frequency expansion laser output by the frequency expansion module 2 passes through the object to be measured 6;

[0074] The data processing module 4 is used to analyze the signal collected by the signal collection module 3 to obtain the frequency response of the object to be measured 6;

[0075] The frequency calibration module 5 is used to receive the frequency laser output by the tunable laser 1 for calibration and measure the frequency output by the laser.

[0076] The difference between this embodiment and embodiment 1 is that the frequency extension module 2 adopts the sum / difference frequency module 202. Specifically, the specific frequency extension scheme using the PPLN periodically poled lithium niobate waveguide as an example is as follows:

[0077] By designing the polarization period range of PPLN, frequency extension of different bands can be achieved. The specific scheme is shown in Table 1 below:

[0078] Table 1 Frequency extension in different bands achieved by PPLN periodically polarized nonlinear crystals

[0079]

[0080] Among them, the laser in the 1260-1680 nanometer band is relatively mature, and the laser in the 630-840 nanometer band is realized by the frequency doubling method of the present invention.

[0081] Based on the nonlinear frequency conversion scheme in the table above, the frequency of the near-infrared laser in the 1260-1680 nanometer band can be extended to 383-10080 nanometers, covering the bandwidth from violet light to mid-infrared. By performing frequency calibration in the near-infrared, the frequency of the laser after frequency conversion can be obtained. After the laser frequency is calibrated, it can be used for spectral analysis.

[0082] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope covered by the present invention.

Claims

1. A spectrum analyzer, characterized in that: include: Tunable laser for outputting frequency laser; A frequency extension module, comprising one or more of a frequency doubling module and a sum / difference frequency module, wherein the frequency extension module is used to receive the frequency laser output by the tunable laser, and perform frequency extension processing using one or more of the frequency doubling module and the sum / difference frequency module, and then output frequency extended laser; A signal acquisition module, used to acquire the signal after the frequency extension laser output by the frequency extension module passes through the object to be measured; The data processing module is used to analyze the signal collected by the signal collection module to obtain the frequency response of the object to be measured.

2. The spectrum analyzer according to claim 1, characterized in that: The frequency doubling module includes a first optical amplifier and a first frequency conversion device; the first frequency conversion device is composed of a nonlinear crystal or a waveguide.

3. The spectrum analyzer according to claim 2, characterized in that: The nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

4. The spectrum analyzer according to claim 1, characterized in that: The sum / difference frequency module includes a pump laser, a second optical amplifier, a third optical amplifier and a second frequency conversion device; the second frequency conversion device is composed of a nonlinear crystal or a waveguide.

5. The spectrum analyzer according to claim 4, characterized in that: The nonlinear crystal includes one or more of a BBO nonlinear crystal, an LBO nonlinear crystal, a PPLN periodically poled nonlinear crystal or waveguide, and a PPKDP periodically poled nonlinear crystal or waveguide.

6. The spectrum analyzer according to any one of claims 1 to 5, characterized in that: The signal acquisition module includes a photoelectric detector and also includes an oscilloscope or an acquisition card.

7. The spectrum analyzer according to claim 6, characterized in that: The data processing module includes a data processing device, and the data processing device includes a computer.

8. The spectrum analyzer according to claim 6, characterized in that: The spectrum analyzer also includes a frequency calibration module, which is used to receive the frequency laser output by the tunable laser for calibration and measure the frequency output by the tunable laser.

9. The spectrum analyzer according to claim 8, characterized in that: The frequency calibration module includes a frequency calibration device, and the frequency calibration device includes one of a fiber ring cavity, a fiber unequal-arm interferometer, and an optical frequency comb.

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