CN111048980A - Wide-range frequency sweeping technology of narrow-linewidth laser - Google Patents
Wide-range frequency sweeping technology of narrow-linewidth laser Download PDFInfo
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- CN111048980A CN111048980A CN201911280828.6A CN201911280828A CN111048980A CN 111048980 A CN111048980 A CN 111048980A CN 201911280828 A CN201911280828 A CN 201911280828A CN 111048980 A CN111048980 A CN 111048980A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
- H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
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Abstract
The invention relates to a wide-range frequency sweep technology of narrow linewidth laser, which adopts a closed-loop feedback optical phase-locked laser frequency sweep method, wherein the closed-loop feedback optical phase-locked laser frequency sweep method obtains an intermediate frequency beat signal through a frequency sweep optical signal sent by a DFB-LD through an unbalanced Mach-Zehnder optical fiber interferometer, compares the intermediate frequency beat signal with a same-frequency low-phase-noise reference signal to obtain an error signal of laser frequency sweep nonlinearity and phase noise for feedback control of laser driving current, and realizes phase locking of the beat signal and the reference signal through closed-loop correction of the laser frequency sweep and the phase noise, thereby obtaining a linear frequency sweep optical signal with effectively suppressed phase noise. The wide-range frequency sweep technology of the narrow linewidth laser provides a closed-loop feedback optical phase-locked laser frequency sweep method, realizes the wide-range frequency sweep of the narrow linewidth laser, effectively corrects the nonlinearity of the frequency sweep, compresses the linewidth of the laser, reduces the phase noise of the laser, and improves the measurement distance, the resolution and the sensitivity of equipment.
Description
Technical Field
The invention relates to the technical field of laser frequency sweeping, in particular to a wide-range frequency sweeping technology of narrow-linewidth laser.
Background
The laser line width and the sweep frequency range respectively determine the distance range and the positioning accuracy which can be measured by OFDR, and the current laser sweep frequency can be divided into two types: firstly, laser internal modulation frequency sweep is realized by tuning laser resonant cavity parameters, and the main technical bottleneck faced by the frequency sweep mode is as follows: the line width of the laser and the sweep frequency range are restricted, the resonant cavity of the narrow line width laser is longer or is a composite cavity, the mode selection mechanism is complex, the sweep frequency range is limited, and the positioning accuracy is limited to centimeter magnitude; on the contrary, the line width of a short-cavity or single-cavity laser capable of supporting large-range frequency sweep is wider, and the measurement distance is limited to the order of hundred meters, so that the OFDR based on the internal modulation frequency sweep cannot be obtained in both the measurement distance and the positioning precision; the laser external modulation frequency sweep realizes optical frequency scanning by an external optical frequency modulator, the technical bottleneck of the method is that the frequency sweep range is limited by the frequency sweep range of a microwave driving signal and the bandwidth of an optical modulator, the frequency sweep range which can be supported by the level of the existing device does not exceed 10GHz, the corresponding OFDR positioning accuracy is limited to the centimeter magnitude, and the external modulation mode has the advantages of good laser coherence and capability of supporting long measuring distance.
The semiconductor laser is a preferred light source of modern optoelectronic devices due to its advantages of small size, convenient frequency control, low price, stability, reliability, etc., and a common distributed feedback semiconductor laser (DFB-LD) can realize a frequency modulation range of about 60GHz and a tuning speed millisecond level by changing a driving current, and can realize frequency tuning of about 200GHz by changing a die temperature, but the tuning speed is slow and can only reach a second level, so that the DFB-LD is adopted as a light source in OFDR, and can realize a distance resolution of sub-millimeter and millimeter level, however, two serious problems are faced: firstly, the laser line width of the DFB-LD can only reach hundreds of KHz-MHz magnitude, the coherence is poor, the optical phase noise is large, the signal-to-noise ratio and the measuring distance of the OFDR are very limited, and only tens of meters and hundreds of meters can be reached; secondly, the relation curve of the output frequency of the DFB-LD and the driving current and the die temperature is nonlinear, and the OFDR distance resolution is deteriorated due to the nonlinear development of frequency scanning based on the driving current and the temperature control.
How to realize narrow linewidth laser of wide-range sweep frequency is a main technical problem in the current OFDR research. A wide-range frequency sweeping technology of narrow-linewidth laser is provided for solving the problem.
Disclosure of Invention
The invention aims to provide a wide-range frequency sweeping technology of narrow-linewidth laser, which aims to solve the problems that the laser linewidth of DFB-LD provided in the background technology can only reach hundreds of KHz-MHz magnitude, the coherence is poor, the optical phase noise is large, the signal-to-noise ratio and the measuring distance of OFDR are very limited, and only reach tens of hundreds of meters; secondly, the relation curve of the output frequency of the DFB-LD and the driving current and the die temperature is nonlinear, and the frequency scanning nonlinear development based on the driving current and the temperature control can cause the problem of the deterioration of the OFDR distance resolution.
A wide-range frequency sweep technology of narrow-linewidth laser adopts a closed-loop feedback optical phase-locked laser frequency sweep method.
Preferably, the closed-loop feedback optical phase-locked laser frequency sweeping method obtains an intermediate frequency beat signal through a frequency sweeping optical signal sent by the DFB-LD through the unbalanced Mach-Zehnder optical fiber interferometer, compares the intermediate frequency beat signal with a low-phase-noise reference signal with the same frequency, and obtains an error signal of laser frequency sweeping nonlinearity and phase noise for feedback control of the laser driving current.
Preferably, the closed-loop feedback optical phase-locked laser frequency sweep realizes phase locking of the beat frequency signal and the reference signal by closed-loop correction of the laser frequency sweep and the phase noise, so that a linear frequency sweep optical signal with effectively suppressed phase noise is obtained.
Preferably, the closed-loop feedback optical phase-locking laser frequency sweeping method compares the beat frequency signal frequency spectrums under the conditions of closed-loop phase-locking and open-loop, and performs data comparison on the beat frequency signal frequency spectrums under the conditions of closed-loop phase-locking and open-loop.
Preferably, the closed-loop feedback optical phase-locked laser frequency sweeping method further compares the change of the beat frequency signal phase with time under the conditions of closed-loop phase locking and open-loop.
Preferably, the closed-loop feedback optical phase-locked laser frequency sweeping method further compares OFDR test results of phase-locked frequency sweeping and phase-unlocked frequency sweeping.
Preferably, the fiber grating sensing system mainly comprises a fiber grating signal processor, a signal transmission system and a fiber grating sensor. The fiber bragg grating sensor acquires physical variable quantity, the optical wavelength is used as a carrier and is transmitted to the signal processor through the optical fiber transmission system, the most direct technology is most commonly used in the optical fiber sensor network by the signal processor, a plurality of signals are distinguished and modulated at the transmitting end to obtain respective optical signals, and then the signals are multiplexed on the same signal to be processed and analyzed, so that physical variable quantity data are acquired. As shown in the following figures. The wavelength division multiplexing technology WDM is transmission in optical fiber, and finally, demultiplexing the multiplexed channels at the receiving end to take out the optical signals of each channel.
Compared with the prior art, the invention has the following beneficial effects: the wide-range frequency sweep technology of the narrow linewidth laser provides a closed-loop feedback optical phase-locking type laser frequency sweep method, realizes the wide-range frequency sweep of the narrow linewidth laser, effectively corrects the nonlinearity of the frequency sweep, compresses the linewidth of the laser, reduces the phase noise of the laser, improves the measurement distance, the resolution and the sensitivity of equipment, effectively compresses the linewidth of the laser, effectively inhibits the phase noise through the closed-loop phase locking with the bandwidth of about 700KHz, obviously improves the coherence of the laser, obviously improves the distance resolution, the measurement distance and the signal to noise ratio through the phase-locking OFDR, and effectively inhibits the phase of a beat frequency signal, and not only the nonlinearity of the frequency sweep but also the phase of the beat frequency signal.
Drawings
FIG. 1 is a schematic diagram of a closed-loop feedback optical phase-locked laser frequency sweep according to the present invention;
FIG. 2 is a power spectrum of the present invention;
FIG. 3 is a graph of the power spectrum of the present invention;
FIG. 4 is a graph of the phase of the beat signal over time in accordance with the present invention;
FIG. 5 is a graph of the results of phase-locked and phase-unlocked swept OFDR tests according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
A wide-range frequency sweep technology of narrow linewidth laser adopts a closed-loop feedback optical phase-locked laser frequency sweep method, provides a closed-loop feedback optical phase-locked laser frequency sweep method (as shown in figure 1), can realize the wide-range frequency sweep of the narrow linewidth laser, improves the distance range and the positioning precision of OFDR, frequency sweep optical signals sent by DFB-LD pass through an unbalanced Mach-Zehnder fiber interferometer to obtain intermediate frequency beat signals, compares the intermediate frequency beat signals with a same-frequency low-phase noise reference signal to obtain error signals of laser frequency sweep nonlinearity and phase noise, is used for feedback control of laser driving current, closed-loop correction of laser frequency sweep and phase noise, realizes phase locking of beat signals and reference signals, thereby obtaining linear sweep optical signals with effectively suppressed phase noise, the closed-loop feedback optical phase-locked laser frequency sweep method compares the beat signal frequency spectrum of closed-loop lock phase with that of open-loop, the closed-loop feedback optical phase-locked laser frequency sweeping method is characterized in that data comparison is carried out on a beat frequency signal frequency spectrum under the conditions of closed-loop phase locking and open-loop, the change of the beat frequency signal phase (corresponding to optical frequency sweeping frequency) along with time under the conditions of closed-loop phase locking and open-loop is compared, the closed-loop feedback optical phase-locked laser frequency sweeping method is also compared with OFDR test results of phase-locked frequency sweeping and phase-unlocked frequency sweeping, the closed-loop feedback optical phase-locked laser frequency sweeping method is provided, the wide-range frequency sweeping of narrow-linewidth laser is realized, the frequency sweeping nonlinearity is effectively corrected, the laser linewidth is compressed, the laser phase noise is reduced, and the measurement distance, the resolution and the.
FIG. 2 is a spectrum of a beat signal with closed-loop phase-lock and open-loop, where a and b in FIG. 2 are power spectra under test conditions of a spectral range (span) of 5MHz, a spectral Resolution (RBW) of 100Hz, and a vertical scale of 10 dB/grid; fig. 3 shows the power spectrum and the phase noise spectrum of the laser under the test conditions that the spectral range (span) is 100KHz, the spectral Resolution (RBW) is 50HZ, and the vertical scale is 10 dB/grid, and the result shows that the laser linewidth is effectively compressed, the phase noise is effectively suppressed, and the coherence of the laser is obviously improved by the closed-loop phase locking with the bandwidth of about 700 KHz.
Fig. 4 shows the change of the beat frequency signal phase (corresponding to the optical frequency sweep frequency) with time under the conditions of closed-loop phase locking and open-loop locking, and the change of the signal phase with time under the condition of open-loop locking shows that the frequency sweep nonlinearity is serious, and the change of the signal phase with time under the condition of closed-loop locking shows that the frequency sweep nonlinearity and the phase of the beat frequency signal are both effectively suppressed.
Fig. 5 is a comparison of the OFDR test results of the phase-locked frequency sweep and the phase-unlocked frequency sweep, and it can be seen that the distance resolution, the measured distance, and the signal-to-noise ratio through the phase-locked OFDR are significantly improved, and the fiber grating sensing system mainly comprises a fiber grating signal processor, a signal transmission system, and a fiber grating sensor. The fiber bragg grating sensor acquires physical variable quantity, the optical wavelength is used as a carrier and is transmitted to the signal processor through the optical fiber transmission system, the most direct technology is most commonly used in the optical fiber sensor network by the signal processor, a plurality of signals are distinguished and modulated at the transmitting end to obtain respective optical signals, and then the signals are multiplexed on the same signal to be processed and analyzed, so that physical variable quantity data are acquired. As shown in the following figures. The wavelength division multiplexing technology WDM is transmission in optical fiber, and finally, demultiplexing the multiplexed channels at the receiving end to take out the optical signals of each channel.
In summary, the technical difficulties involved in the frequency sweeping scheme mainly include: ultra-low noise, broadband modulation laser drive technology; a high-stability laser temperature control technology; a high-stability unbalanced Mach-Zehnder optical fiber interference technology; low-noise broadband light balance receiving technology; low noise, broadband optical phase lock technology; the patent provides a closed-loop feedback optical phase-locked laser frequency sweeping method, which realizes wide-range frequency sweeping of narrow-linewidth laser, effectively corrects frequency sweeping nonlinearity, compresses laser linewidth, reduces laser phase noise, and improves measurement distance, resolution and sensitivity of equipment.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical scope of the present invention and the equivalent alternatives or modifications according to the technical solution and the inventive concept of the present invention within the technical scope of the present invention.
Claims (7)
1. A wide-range frequency sweep technology of narrow linewidth laser is characterized in that a closed-loop feedback optical phase-locked laser frequency sweep method is adopted.
2. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: according to the closed-loop feedback optical phase-locked laser frequency sweeping method, a frequency sweeping optical signal sent by a DFB-LD passes through an unbalanced Mach-Zehnder optical fiber interferometer to obtain an intermediate frequency beat signal, the intermediate frequency beat signal is compared with a same-frequency low-phase-noise reference signal, and an error signal of laser frequency sweeping nonlinearity and phase noise is obtained and is used for feedback control of laser driving current.
3. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: the closed-loop feedback optical phase-locked laser frequency sweeping realizes the phase locking of the beat frequency signal and the reference signal by closed-loop correction of the laser frequency sweeping and the phase noise, thereby obtaining a linear frequency sweeping optical signal with effectively suppressed phase noise.
4. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: the closed-loop feedback optical phase-locking type laser frequency sweeping method compares the beat frequency signal frequency spectrums under the conditions of closed-loop phase locking and open-loop, and performs data comparison on the beat frequency signal frequency spectrums under the conditions of closed-loop phase locking and open-loop.
5. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: the closed-loop feedback optical phase-locking type laser frequency sweeping method also compares the change of the phase of the beat frequency signal along with the time under the conditions of closed-loop phase locking and open-loop.
6. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: the closed-loop feedback optical phase-locked laser frequency sweeping method also compares the OFDR test results of phase-locked frequency sweeping and phase-unlocked frequency sweeping.
7. A wide range frequency sweep technique for narrow linewidth lasers as claimed in claim 1 wherein: the fiber grating sensing system mainly comprises a fiber grating signal processor, a signal transmission system and a fiber grating sensor. The fiber bragg grating sensor acquires physical variable quantity, the optical wavelength is used as a carrier and is transmitted to the signal processor through the optical fiber transmission system, the most direct technology is most commonly used in the optical fiber sensor network by the signal processor, a plurality of signals are distinguished and modulated at the transmitting end to obtain respective optical signals, and then the signals are multiplexed on the same signal to be processed and analyzed, so that physical variable quantity data are acquired. As shown in the following figures. The wavelength division multiplexing technology WDM is transmission in optical fiber, and finally, demultiplexing the multiplexed channels at the receiving end to take out the optical signals of each channel.
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| US11119213B2 (en) * | 2019-02-27 | 2021-09-14 | Aeva, Inc. | Method for generating a linear chirp from a laser light source |
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| CN105006736A (en) * | 2015-05-08 | 2015-10-28 | 上海交通大学 | Frequency modulated continuous wave (FMCW) frequency sweep non-leaner calibration system based on closed loop control and FMCW frequency sweep non-leaner calibration method based on closed loop control |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US11119213B2 (en) * | 2019-02-27 | 2021-09-14 | Aeva, Inc. | Method for generating a linear chirp from a laser light source |
| US11914038B2 (en) | 2019-02-27 | 2024-02-27 | Aeva, Inc. | Locking a self-homodyne mixed beat frequency to an external frequency in a LIDAR system |
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