WO2024067152A1 - 激光系统的本征频率探测、开关控制及截止频率稳定方法 - Google Patents

激光系统的本征频率探测、开关控制及截止频率稳定方法 Download PDF

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WO2024067152A1
WO2024067152A1 PCT/CN2023/118995 CN2023118995W WO2024067152A1 WO 2024067152 A1 WO2024067152 A1 WO 2024067152A1 CN 2023118995 W CN2023118995 W CN 2023118995W WO 2024067152 A1 WO2024067152 A1 WO 2024067152A1
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laser
frequency
local
detection
light source
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PCT/CN2023/118995
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French (fr)
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郭海润
查子民
牟成博
戴礼龙
孙苏皖
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上海大学
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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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • 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
    • 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
    • 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
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude

Definitions

  • the invention belongs to the field of laser technology, and in particular relates to a method for detecting the intrinsic frequency, controlling the switch and stabilizing the cut-off frequency of a laser system.
  • any system has an eigenfrequency, and the system can induce a change of state when operating at this frequency. Therefore, measuring the eigenfrequency of the system is an important way to characterize the characteristics of the system.
  • the measurement of the eigenfrequency requires the system to be in an online working state, and there are currently few technologies that can accomplish this.
  • pulsed lasers have the characteristics of wide spectrum and high power in a short time, and play an important role in laser detection, laser manufacturing and other fields.
  • the generation of ultrashort pulse lasers relies on laser mode locking technology.
  • the spontaneous pulse forming process requires a certain amount of establishment time and may be accompanied by extremely high-power pre-pulse signals, which can damage the laser and the application system. Therefore, it is very necessary to develop effective eigenfrequency switching control technology, detection technology and cutoff frequency stabilization methods for ultrashort pulse laser systems.
  • the present invention aims to provide a method for detecting the eigenfrequency, controlling the switch and stabilizing the cutoff frequency of a laser system.
  • the laser system is a non-local pumped ultrashort pulse laser system, including a non-local pump light source, a laser oscillator cavity, an optoelectronic detection component, a feedback control circuit and a local detection light source.
  • the frequency or wavelength of the non-local pump light source is outside the frequency or wavelength range of the output pulse laser;
  • the frequency or wavelength of the local detection light source is within the frequency or wavelength range of the output pulse laser and is generally a single-frequency laser component that emits continuous light, and can achieve frequency or wavelength tuning, or can achieve frequency tuning and frequency scanning functions through an external electro-optical, acousto-optical or other optical modulator, and the tuning method is an analog or digital electronic control method;
  • the laser oscillator cavity includes a gain medium, an active or passive light intensity modulation device, and an optical reflection device, and is applicable to a free space laser cavity, a fiber laser cavity, an optical body medium cavity, and a micro-nano optical waveguide resonant cavity;
  • the photoelectric detection component includes an optical detection component and an electrical detection component, wherein the optical detection component includes a spectrometer, a spectrum analyzer, an optical power meter, and an optical autocorrelator, and the electrical detection component includes a photoelectric converter, a splitter, a filter, an oscilloscope, and an electronic spectrometer.
  • the optical detection component includes a spectrometer, a spectrum analyzer, an optical power meter, and an optical autocorrelator
  • the electrical detection component includes a photoelectric converter, a splitter, a filter, an oscilloscope, and an electronic spectrometer.
  • An eigenfrequency detection method for a non-locally pumped ultrashort pulse laser system comprises the following steps:
  • Step 1 Turn on the non-local pump light source and inject it into the laser oscillator cavity.
  • the laser oscillator cavity By adjusting the intensity of the pump light source, the laser oscillator cavity generates a pulsed laser output, that is, mode-locked pulse laser generation is achieved;
  • Step 2 While the pulsed laser is outputting normally, turn on the local detection light source and start the laser frequency scan;
  • Step 3 Electrically detect the output pulse laser. After the laser passes through the photoelectric converter and low-pass filter, one or more "resonance peak" waveforms are observed on the oscilloscope. The waveform presents a Lorentz line shape, which is the inherent characteristic of the laser system.
  • Step 4 Read the frequency or wavelength information of the local detection laser, obtain the frequency at the peak of the resonance peak in step 3, and measure the intrinsic frequency of the laser system.
  • the mode-locked pulse laser is output by a classic mode-locked pulse laser system composed of a non-local pump light source and a laser oscillator cavity.
  • a switch control method is used for a non-locally pumped ultrashort pulse laser system. Based on the fact that local probe light at the resonant frequency has an inhibitory effect on the generation of ultrashort pulses in the laser oscillator cavity, the switching control operation of the output laser pulse can be achieved by controlling the frequency or power of the probe laser.
  • the switch control includes the following steps:
  • Step 1 Measure the intrinsic resonance peak
  • Step 2 Stop the frequency scanning of the local detection laser, and set the frequency or wavelength of the local detection laser to the peak value of the resonance peak, or control the frequency tuning state of the laser through a feedback circuit so that the laser frequency or wavelength is always at the peak value of the resonance peak;
  • Step 3 Adjust the power of the local probe laser to a high level until the pulsed laser of the laser oscillator cavity The light stops outputting, which corresponds to the “off” state of the laser;
  • Step 4 Turn off the local detection laser, or move the laser frequency or wavelength out of the peak of the resonance peak, and the laser oscillator cavity resumes the pulsed laser output, which corresponds to the laser "on" state.
  • the electronically controlled frequency tuning function contained in the local detection laser source can be used in combination with a feedback control circuit to quickly and arbitrarily switch the above switching state.
  • a cutoff frequency stabilization method is used for a non-locally pumped ultrashort pulse laser system. Through a feedback control circuit, a local detection light source is controlled to always be located at the resonant frequency of the laser oscillation cavity, and a stable frequency deviation is always maintained between the output frequency of the laser and the resonant frequency.
  • the cutoff frequency stabilization method includes the following steps:
  • Step 1 The pulsed laser output by the laser oscillator corresponds to a set of discrete, equally spaced frequency elements in the frequency domain;
  • Step 2 Select one of the frequency elements and perform frequency shift through an electro-optical modulator, where the shift amount is controlled by an external reference signal source;
  • Step 3 The selected frequency element is injected into the laser oscillation cavity again as a local detection laser;
  • Step 4 The intensity of the non-local pump light source is regulated by a feedback control circuit so that the local detection laser is always located at the intrinsic frequency of the laser system, thereby stabilizing the deviation between the selected laser frequency element and the system resonant frequency, i.e., the cutoff frequency, which is equal to the external reference signal source.
  • the offset can be derived from a standard low-noise ultra-stable RF signal source, or an atomic clock; the frequency tuning of the local detection light source can be controlled by the current of the non-local pump light source.
  • the present invention has the following advantages:
  • the proposed method for detecting the eigenfrequency of a non-locally pumped ultrashort pulse laser system can obtain the eigenfrequency of the laser and play a better role in the fields of laser detection and laser manufacturing.
  • the proposed switching control method for the non-locally pumped ultrashort pulse laser system is independent of the laser wavelength, bandwidth, power and other performance parameters, and is compatible with laser oscillator cavities of different transmission media such as space, optical fiber, micro-nano optical waveguide, and can achieve a higher switching rate.
  • the proposed cutoff frequency stabilization method for non-locally pumped ultrashort pulse laser system is used for laser frequency stabilization.
  • this method can be completed within the existing frequency range of the laser without the need for external frequency extension components. Therefore, it is suitable for low-power ultrashort pulse lasers to achieve frequency stabilization.
  • FIG1 is a configuration diagram of a non-locally pumped ultrashort pulse laser system in the present invention.
  • FIG2 is a schematic diagram showing the configuration of a non-locally pumped ultrashort pulse laser system according to the present invention
  • FIG3 is a schematic diagram of the feedback control circuit implementation in the present invention.
  • Figure 4 (a) is the time domain superposition signal diagram of the measured system resonance peak and laser pulse; (b) is the time domain signal diagram after the local detection laser is locked with the system resonance peak; (c) is the beat frequency spectrum diagram formed by the local detection laser and the partial frequency of the mode-locked pulse laser after the local detection laser is locked with the system resonance peak.
  • FIG5 (a) is a pulse signal result diagram of the ultrashort pulse laser switch operation test implemented; (b) is a frequency modulation signal diagram of the ultrashort pulse laser switch operation test implemented;
  • 1-980nm laser light source 2-980/1550nm wavelength division multiplexer; 3-fiber laser oscillator cavity; 4-erbium-doped fiber; 5-1550nm tunable continuous laser light source; 6-2 ⁇ 2 coupler; 7-fiber polarization controller; 8-saturable absorber; 9-fiber isolator; 10-feedback control circuit based on PDH technology; 11-electro-optic phase modulator; 12-acousto-optic modulator.
  • a non-locally pumped ultrashort pulse laser system includes a non-locally pumped light source, a laser oscillator cavity, an optoelectronic detection component, a feedback control circuit, and a local detection light source.
  • a non-local pumped ultrashort pulse laser system configuration wherein the non-local pump light source is a laser light source 1 with a wavelength of 980nm, which is injected into the laser oscillator cavity 3 through a 980/1550nm wavelength division multiplexer 2.
  • the laser oscillator cavity is a fiber laser oscillator cavity 3, which includes an erbium-doped fiber 4 excited by a 980nm light source. Intracavity gain in the 1550nm band is generated under the condition of a saturable absorber connected in the cavity to help achieve passive mode-locked pulse laser generation in the 1550nm band.
  • the pulse width is generally in the sub-picosecond level, that is, an ultrashort pulse.
  • the local detection light source is a tunable continuous laser light source 5 with a wavelength of about 1550nm.
  • the light source supports electronically controlled laser frequency tuning, which is injected into the laser oscillation cavity through a 2 ⁇ 2 coupler 6, and the pulsed laser in the cavity is output at the other output end of the 2 ⁇ 2 coupler 6.
  • the output intracavity laser is photoelectrically characterized, wherein the electrical characterization includes using a photoelectric converter to convert the optical signal into an electrical signal, performing time domain signal measurement and electronic spectrum measurement, and the optical characterization includes spectrum measurement and optical power measurement.
  • the feedback control circuit 10 adopts the classic Pound-Drever-Hall (PDH) technology.
  • the output port of this circuit part includes an output RF modulation signal, which modulates the local detection laser through the electro-optical modulator 11.
  • a feedback signal is used to control the local detection laser to perform frequency tuning to compensate for the frequency jitter of the system.
  • the input port includes an input signal output by a laser oscillator cavity after photoelectric conversion. This signal essentially contains the signal component of the local detection light modulated by RF after passing through the fiber laser oscillator cavity.
  • the specific operation steps of the intrinsic frequency detection method of the non-locally pumped ultrashort pulse laser system are as follows:
  • Step 1 Turn on the 980nm laser light source 1, control the laser power to 117mW, and inject it into the fiber laser oscillator cavity.
  • the laser oscillator cavity can spontaneously generate a mode-locked pulse laser.
  • the pulse laser is output through the 2 ⁇ 2 coupler 6.
  • the pulse repetition frequency is 20.22MHz
  • the pulse time period is about 50ns
  • the laser output power is about 162 ⁇ W
  • the spectral center wavelength is 1565.49nm.
  • Step 2 Turn on the tunable continuous laser light source 5, with a power of about 23.57 ⁇ W, and drive it to scan the laser frequency with a triangle wave electrical signal, with a scanning range of about 125 MHz, a central wavelength of 1565.49 nm, and a scanning speed of 10 Hz.
  • the output laser of the laser oscillator cavity is electrically characterized, and with the help of an oscilloscope, it can be observed that multiple waveforms showing Lorentz line shapes are superimposed on the laser pulse in time (a section of the waveform is shown in FIG. 4 a), and the Lorentz line shape is the resonance peak of the mode-locked laser system.
  • Step 3 Connect the feedback control circuit 10 based on PDH technology, where the RF modulation signal frequency is set to 9MHz, modulate the local detection laser through an electro-optical phase modulator 11, and the output feedback signal is connected to the laser as the frequency tuning drive signal of the local detection light source.
  • the frequency of the local detection laser can always be kept at the peak of the resonance peak (frequency locking), and the pulse signal amplitude of the observed laser time domain electrical signal is kept at the bottom level of the resonance peak (as shown in Figure 4b).
  • Step 4 Couple the pulsed laser output from the laser oscillator cavity with the frequency-locked local detection light, and observe its electronic spectrum through photoelectric conversion. It can be observed that a pair of narrow-band frequency components appear on the spectrum, with frequencies of 7.45MHz and 12.77MHz respectively (as shown in Figure 4c), and the sum of the two frequencies is equal to the repetition frequency of the mode-locked pulse laser. This pair of frequencies is the beat frequency signal of the local detection laser and the partial frequency of the mode-locked pulse laser, indicating that there is a difference between the intrinsic resonant frequency of the laser system and the output laser frequency, that is, there is a frequency detuning amount of 7.45MHz.
  • the specific operation steps are as follows:
  • Step 1 Before the tunable continuous laser is injected into the laser oscillation cavity, an acousto-optic modulator 12 is connected to achieve fast frequency switching, that is, the switch signal is connected.
  • Step 2 According to the intrinsic frequency detection method of the non-local pump pulse laser system, the local detection light source after the acousto-optic modulator 12 is biased and locked with the system resonance frequency (keep the frequency consistent). At this time, the modulation frequency loaded in the acousto-optic modulation is 148MHz, that is, the frequency deviation.
  • the local detection laser power is about 100 ⁇ W. At this power, due to the large depth of the system resonance peak, the output of the mode-locked pulse laser is suppressed and the system is in the "off" state.
  • Step 3 By changing the modulation signal frequency loaded by the acousto-optic modulator 12 to 152 MHz, the offset local detection laser frequency is moved out of the resonant frequency. The mode-locked pulse laser output is restored, and the system is now in the "on" state.
  • Step 4 Using the frequency modulation electronic switch, the modulation signal frequency loaded into the AOM 12 can be quickly and arbitrarily switched, thereby realizing any controllable system switch.
  • FIG5 shows the switch control effect of a system with double pulses at the input within a local time.
  • the specific operation steps are as follows:
  • Step 1 Turn on the 980nm laser light source 1, control the laser power to 117mW, and inject it into the fiber laser oscillator cavity, and the laser oscillator cavity spontaneously generates a mode-locked pulse laser.
  • the pulse laser is output through the 2 ⁇ 2 coupler 6.
  • electrical characterization it can be known that the pulse repetition frequency is 20.22MHz, and the pulse time period is about 50ns.
  • the laser output power is about 162 ⁇ W, and the central wavelength of the spectrum is 1565.49nm, which corresponds to a set of discrete, equally spaced frequency elements in the frequency domain;
  • Step 2 Connect the feedback control circuit 10 based on PDH technology and select a frequency element in the frequency domain.
  • the frequency is shifted by the electro-optic modulator 11, and the shift amount is controlled by an external reference signal source;
  • Step 3 The selected frequency element is injected into the laser oscillation cavity again as a local detection laser;
  • Step 4 The intensity of the 980nm laser light source 1 is regulated by the feedback control circuit 10 so that the local detection laser is always located at the intrinsic frequency of the laser system, thereby stabilizing the deviation between the selected laser frequency element and the system resonant frequency, that is, the cutoff frequency, which is equal to the external reference signal source.

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Abstract

一种激光系统的本征频率探测、开关控制及截止频率稳定方法，本征频率探测方法通过开启非局域泵浦光源，注入激光振荡腔，开启本地探测光源，最终获得激光本征频率；开关控制方法基于位于谐振频率处的本地探测光对于激光振荡腔内超短脉冲的抑制作用，实现开关控制操作；截止频率稳定方法通过反馈控制电路，控制本地探测光源始终位于激光振荡腔的谐振频率处，在激光的输出频率与谐振频率之间始终保持稳定的频率偏差。

Description

激光系统的本征频率探测、开关控制及截止频率稳定方法 技术领域
本发明属于激光技术领域，具体涉及激光系统的本征频率探测、开关控制及截止频率稳定方法。
背景技术
任何系统均有本征频率，系统工作在该频率上可以诱发状态的改变。因此测量系统的本征频率是表征系统特性的重要方式。对于超短脉冲激光系统，本征频率的测量要求系统处于在线工作状态，目前鲜有技术可以完成。同时，脉冲式激光具有频谱宽、短时功率高等特点，在激光探测、激光制造等领域具有重要作用。超短脉冲激光的产生依靠激光锁模技术，脉冲自发成形过程需要一定的建立时间，并可能伴随功率极强的预脉冲信号，对激光器和应用系统造成破坏。因此，开发有效的超短脉冲激光系统本征频率开关控制技术、探测技术以及截止频率稳定方法十分必要。
发明内容
为了解决上述问题，本发明旨在提供激光系统的本征频率探测、开关控制及截止频率稳定方法。
为了实现上述目的，本发明以下技术方案：激光系统为非局域泵浦超短脉冲激光系统，包括非局域泵浦光源、激光振荡腔、光电学探测组件、反馈控制电路及本地探测光源。
所述非局域泵浦光源的频率或波长在输出脉冲激光的频率或波长范围之外；所述本地探测光源的频率或波长在输出脉冲激光的频率或波长范围之内且一般是单频激光元器件，发出连续光，可以实现频率或波长的调谐，或者可以通过外加电光、声光等光学调制器实现频率调谐和频率扫描功能，调谐方式为模拟或数字电子控制方式；
所述激光振荡腔包括了增益介质、主动或被动的光强调制器件、以及光学反射器件，且适用于自由空间激光腔、光纤激光腔、光学体介质腔以及微纳光学波导谐振腔；
所述光电学探测组件包括光学探测组件和电学探测组件，其中光学探测组件包括分光器、光谱分析仪、光功率计、光学自相关仪，电学探测组件包括光电转换器、分路器、滤波器、示波器、电子频谱仪。
一种本征频率探测方法用于非局域泵浦超短脉冲激光系统，包括以下步骤：
步骤1：开启非局域泵浦光源，注入激光振荡腔，通过调节泵浦光源的强度使激光振荡腔产生脉冲式的激光输出，即实现锁模脉冲激光产生；
步骤2：在脉冲式激光正常输出同时，开启本地探测光源，并开启激光频率扫描；
步骤3：对输出脉冲激光进行电学探测，激光经光电转换器、低通滤波器后在示波器中观察到一个或多个“谐振峰”波形，波形呈现出洛伦兹线形，该波形即激光器系统的内在特征；
步骤4：读取本地探测激光的频率或波长信息，获取步骤3中谐振峰的峰值处频率，即测得了激光器系统的本征频率。
所述锁模脉冲激光是由非局域泵浦光源和激光振荡腔组成经典的锁模脉冲激光系统输出的。
一种开关控制方法用于非局域泵浦超短脉冲激光系统，基于位于谐振频率处的本地探测光对于激光振荡腔内超短脉冲的产生具有抑制作用，通过控制探测激光的频率或功率，可以实现对输出激光脉冲的开光控制操作，开关控制包括以下步骤：
步骤1：测得本征谐振峰；
步骤2：停止本地探测激光的频率扫描，并将本地探测激光的频率或波长设定至谐振峰峰值处，或通过反馈电路控制激光器的频率调谐状态，使激光频率或波长始终位于谐振峰的峰值处；
步骤3：调节本地探测激光的功率位于高水平，直至激光振荡腔的脉冲式激 光停止输出，即对应了激光器“关”状态；
步骤4:关闭本地探测激光器，或将激光器频率或波长移出谐振峰的峰值处，激光振荡腔恢复脉冲式激光输出，即对应了激光器“开”状态。
可利用本地探测激光源所包含的电子控制频率调谐功能，结合反馈控制电路，可以快速、任意地切换上述开关状态。
一种截止频率稳定方法用于非局域泵浦超短脉冲激光系统，通过反馈控制电路，控制本地探测光源始终位于激光振荡腔的谐振频率处，在激光的输出频率与谐振频率之间始终保持一个稳定的频率偏差，截止频率稳定方法包括以下步骤：
步骤1：激光振荡器输出的脉冲式激光，其频域上对应了一组离散、等间隔的频率元素；
步骤2：选中其中的一个频率元素，通过电光调制器进行频率偏移，偏移量由外部参考信号源控制；
步骤3：该被选中的频率元素，作为本地探测激光，再次注入激光振荡腔中；
步骤4：通过反馈控制电路调控非局域泵浦光源的强度，使本地探测激光始终位于激光器系统的本征频率处，由此稳定该被选中的激光频率元素与系统谐振频率的偏差量，即截止频率，该偏差量等于外部参考信号源。
所述偏移量可以源自标准的低噪声超稳射频信号源，或原子钟；所述本地探测光源的频率调谐可以通过非局域泵浦光源的电流控制。
与现有技术相比，本发明具有以下优势：
1.提出的非局域泵浦超短脉冲激光系统的本征频率探测方法，该方法能获得激光本征频率，在激光探测、激光制造等领域发挥更好的作用。
2.提出的非局域泵浦超短脉冲激光系统的开光控制方法，该方法与激光波长、带宽、功率等性能参数均无关，并且兼容空间、光纤、微纳光学波导等不同传输介质的激光振荡腔，同时可以实现较大的开关速率。
3.提出的非局域泵浦超短脉冲激光系统截止频率稳定方法，该方法用于激光频率稳定，特别是该种方式可以在激光既有的频率范围内完成，无需外加频率扩展部件，因此适合低功率水平的超短脉冲激光实现频率稳定。
附图说明
为了更清楚地说明本发明具体实施例中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明中的非局域泵浦超短脉冲激光系统构型图；
图2为本发明中的非局域泵浦超短脉冲激光系统构型实施原理图；
图3为本发明中的反馈控制电路实施原理图；
图4中(a)为测得的系统谐振峰与激光脉冲的时域叠加信号图；(b)为本地探测激光与系统谐振峰锁定后的时域信号图；(c)为本地探测激光与系统谐振峰锁定后，其与锁模脉冲激光部分频率形成的拍频频谱图。
图5中(a)为所实现的超短脉冲激光开关操作测试脉冲信号结果图；(b)为所实现的超短脉冲激光开关操作测试调频信号图；
图中，1-980nm激光光源；2-980/1550nm波分复用器；3-光纤激光振荡腔；4-掺铒光纤；5-1550nm可调谐连续激光光源；6-2×2耦合器；7-光纤偏振控制器；8-可饱和吸收器；9-光纤隔离器；10-基于PDH技术的反馈控制电路；11-电光相位调制器；12-声光调制器。
具体实施方式
下面结合附图和具体实施例对本发明作进一步的说明，但不应就此理解为本发明所述主题的范围仅限于以下的实施例，在不脱离本发明上述技术思想情况下，凡根据本领域普通技术知识和惯用手段做出的各种修改、替换和变更，均包括在本发明的范围内。
参照图1，一种非局域泵浦超短脉冲激光系统，包括非局域泵浦光源、激光振荡腔、光电学探测组件、反馈控制电路及本地探测光源。
参照图2，一种非局域泵浦超短脉冲激光系统构型，其中的非局域泵浦光源为波长980nm的激光光源1，通过980/1550nm波分复用器2注入到激光振荡腔内3。激光振荡腔为光纤激光振荡腔3，其中包括掺铒光纤4在980nm光源激励 下产生1550nm波段的腔内增益，腔内还接入了可饱和吸收体助于实现1550nm波段的被动锁模脉冲激光产生，脉冲宽度一般在亚皮秒量级，即为超短脉冲。
本地探测光源为波长在1550nm附近的可调谐连续激光光源5，该光源内部支持电子控制的激光频率调谐，通过一个2×2耦合器6注入激光振荡腔，并在此2×2耦合器6的另一个输出端输出腔内的脉冲激光。对于输出的腔内激光进行光电学表征，其中电学表征包括使用光电转换器将光学信号转为电学信号，进行时域信号测量、电子频谱测量，光学表征包括光谱测量，光功率测量。
参照图3，反馈控制电路10，采用了经典的Pound-Drever-Hall(PDH)技术，该电路部分的输出端口包括输出一路射频调制信号，经电光调制器11对本地探测激光进行调制，一路反馈信号用于控制本地探测激光进行频率调谐补偿系统的频率抖动，输入端口包括输入一路激光振荡腔输出的经过光电转换的信号，该信号本质上包含了经射频调制的本地探测光透过光纤激光振荡腔后的信号成分。
对于非局域泵浦超短脉冲激光系统的本征频率探测方法在实施例中，具体操作步骤如下：
步骤1：打开980nm激光光源1，控制激光功率为117mW，注入到光纤激光振荡腔内，激光振荡腔可以自发产生锁模脉冲激光。该脉冲激光经过2×2耦合器6输出，经电学表征，可以获知脉冲的重复频率为20.22MHz，脉冲时间周期约为50ns，经光学表征，可以获知激光输出功率约为162μW，光谱中心波长为1565.49nm。
步骤2：打开可调谐连续激光光源5，功率约为23.57μW，并以一个三角波电信号驱动在激光频率扫描，扫描范围约125MHz，中心波长为1565.49nm，扫描速度为10Hz。此时对激光振荡腔的输出激光进行电学表征，借助示波器可以在时间上观察到多个呈现出洛伦兹线形的波形与激光脉冲相互叠加(其中的一段波形如图4a所示)，该洛伦兹线形即为锁模激光器系统的谐振峰。
步骤3：接入基于PDH技术的反馈控制电路10，其中设置射频调制信号频率为9MHz，通过一个电光相位调制器11对本地探测激光进行调制，输出的反馈信号作为本地探测光源的频率调谐驱动信号接入激光器。通过合理配置反馈控制电路10的内部参数，可以将本地探测激光的频率始终保持在谐振峰的峰值处(频率锁定)，此时观察到的激光时域电信号，其中的脉冲信号幅度保持在谐振峰的底部水平(如图4b所示)。
步骤4：将激光振荡腔输出的脉冲激光与频率锁定的本地探测光耦合，经光电转换观察其电子频谱，可以观察到频谱上出现了一对窄带的频率成分，频率分别为7.45MHz和12.77MHz(如图4c所示)，两者频率之和等于锁模脉冲激光的重复频率。这对频率即为本地探测激光与锁模脉冲激光部分频率的拍频信号，表明激光系统的本征谐振频率与输出激光频率存在差异，即存在频率失谐量，为7.45MHz。
对于所述非局域泵浦脉冲激光的开关控制方法，在实施例中，具体操作步骤如下：
步骤1：可调谐连续激光器在注入激光振荡腔之前，接入一个声光调制器12用于实现快速的频率切换，即开关信号接入。
步骤2：按照非局域泵浦脉冲激光系统的本征频率探测方法，实现声光调制器12偏频后的本地探测光源与系统谐振频率的锁定(保持频率一致)，此时声光调制中加载的调制频率为148MHz,即频率偏差量。本地探测激光功率约为100μW,此功率下，由于系统谐振峰深度较大，锁模脉冲激光的输出被抑制，系统处于“关闭”状态。
步骤3：通过改变声光调制器12加载的调制信号频率至152MHz，即将偏频后的本地探测激光频率移出谐振频率处。锁模脉冲激光输出恢复，此时系统处于“开启”状态。
步骤4：利用调频电子开关，可以快速、任意地切换加载到声光调制器12的调制信号频率，由此实现任意可控的系统开关
如图5所示为输处为双脉冲的系统在局部时间内的开关控制效果。
对于所述非局域泵浦脉冲激光的截止频率稳定方法，在实施例中，具体操作步骤如下：
步骤1：打开980nm激光光源1，控制激光功率为117mW，注入到光纤激光振荡腔内，激光振荡腔自发产生锁模脉冲激光。该脉冲激光经过2×2耦合器6输出，经电学表征，可以获知脉冲的重复频率为20.22MHz，脉冲时间周期约为50ns，经光学表征，可以获知激光输出功率约为162μW，光谱中心波长为1565.49nm，其频域上对应了一组离散、等间隔的频率元素；
步骤2：接入基于PDH技术的反馈控制电路10，选中频域上的一个频率元 素，通过电光调制器11进行频率偏移，偏移量由外部参考信号源控制；
步骤3：该被选中的频率元素，作为本地探测激光，再次注入激光振荡腔中；
步骤4：通过反馈控制电路10调控980nm激光光源1的强度，使本地探测激光始终位于激光器系统的本征频率处，由此稳定该被选中的激光频率元素与系统谐振频率的偏差量，即截止频率，该偏差量等于外部参考信号源。
以上对本发明所提供的一种非局域泵浦超短脉冲激光系统的开关控制方法、本征频率探测方法及截止频率稳定方法进行了详细介绍，本文中应用了具体个例对本发明的结构及工作原理进行了阐述，以上实施例的说明只是用于帮助理解本发明的方法及核心思想。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以对本发明进行若干改进和修饰，这些改进和修饰也落入本发明权利要求保护的范围内。

Claims (9)

  1. 激光系统为非局域泵浦超短脉冲激光系统，其特征在于：包括非局域泵浦光源、激光振荡腔、光电学探测组件、反馈控制电路及本地探测光源。
  2. 根据权利要求1所述的非局域泵浦超短脉冲激光系统，其特征在于：所述非局域泵浦光源的频率或波长在输出脉冲激光的频率或波长范围之外；所述本地探测光源的频率或波长在输出脉冲激光的频率或波长范围之内且一般为单频率激光元器件，发出连续光，可以实现频率或波长的调谐，或者可以通过外加电光、声光等光学调制器实现频率调谐和频率扫描功能，调谐方式为模拟或数字电子控制方式；
    所述激光振荡腔包括了增益介质、主动或被动的光强调制器件、以及光学反射器件，且适用于自由空间激光腔、光纤激光腔、光学体介质以及微纳光学波导谐振腔。
  3. 根据权利要求1所述的非局域泵浦超短脉冲激光系统，其特征在于：所述光电学探测组件包括光学探测组件和电学探测组件，其中光学探测组件包括分光器、光谱分析仪、光功率计、光学自相关仪，电学探测组件包括光电转换器、分路器、滤波器、示波器、电子频谱仪。
  4. 一种本征频率探测方法，用于权利要求1-3任一项所述的非局域泵浦超短脉冲激光系统，其特征在于，本征频率探测方法包括以下步骤：
    步骤1：开启非局域泵浦光源，注入激光振荡腔，通过调节泵浦光源的强度使激光振荡腔产生脉冲式的激光输出，即实现锁模脉冲激光产生；
    步骤2：在脉冲式激光正常输出同时，开启本地探测光源，并开启激光频率扫描；
    步骤3：对输出脉冲激光进行电学探测，激光经光电转换器、低通滤波器后在示波器中观察到一个或多个“谐振峰”波形，波形呈现出洛伦兹线形，该波形即激光器系统的内在特征；
    步骤4：读取本地探测激光的频率或波长信息，获取步骤3中谐振峰的峰值处频率，即测得了激光器系统的本征频率。
  5. 根据权利要求4所述的本征频率探测方法，其特征在于：所述锁模脉冲激光是由非局域泵浦光源和激光振荡腔组成经典的锁模脉冲激光系统输出的。
  6. 一种激光系统的开关控制方法，用于权利要求1-3任一项所述的非局域泵 浦超短脉冲激光系统，其特征在于：基于位于谐振频率处的本地探测光对于激光振荡腔内超短脉冲的产生具有抑制作用，通过控制探测激光的频率或功率，可以实现对输出激光脉冲的开光控制操作，开关控制包括以下步骤：
    步骤1：基于权利要求4所述的本征频率探测方法,测得本征谐振峰；
    步骤2：停止本地探测激光的频率扫描，并将本地探测激光的频率或波长设定至谐振峰峰值处，或通过反馈电路控制激光器的频率调谐状态，使激光频率或波长始终位于谐振峰的峰值处；
    步骤3：调节本地探测激光的功率位于高水平，直至激光振荡腔的脉冲式激光停止输出，即对应了激光器“关”状态；
    步骤4:关闭本地探测激光器，或将激光器频率或波长移出谐振峰的峰值处，激光振荡腔恢复脉冲式激光输出，即对应了激光器“开”状态。
  7. 根据权利要求6所述的开光控制方法，其特征在于：可利用本地探测激光源所包含的电子控制频率调谐功能，结合反馈控制电路，可以快速、任意地切换上述开关状态。
  8. 一种截止频率稳定方法，用于权利要求1-3任一项所述的非局域泵浦超短脉冲激光系统，其特征在于：通过反馈控制电路，控制本地探测光源始终位于激光振荡腔的谐振频率处，在激光的输出频率与谐振频率之间始终保持一个稳定的频率偏差，截止频率稳定方法包括以下步骤：
    步骤1：激光振荡器输出的脉冲式激光，其频域上对应了一组离散、等间隔的频率元素；
    步骤2：选中其中的一个频率元素，通过电光调制器进行频率偏移，偏移量由外部参考信号源控制；
    步骤3：该被选中的频率元素，作为本地探测激光，再次注入激光振荡腔中；
    步骤4：通过反馈控制电路调控非局域泵浦光源的强度，使本地探测激光始终位于激光器系统的本征频率处，由此稳定该被选中的激光频率元素与系统谐振频率的偏差量，即截止频率，该偏差量等于外部参考信号源。
  9. 根据权利要求8所述的截止频率稳定方法，其特征在于：所述偏移量可以源自标准的低噪声超稳射频信号源，或原子钟；所述本地探测光源的频率调谐可 以通过非局域泵浦光源的电流控制。
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