CN106936070B - An all-optical pure frequency modulation system based on quantum cascade lasers - Google Patents

Abstract

The invention discloses an all-optical pure frequency modulation system based on a quantum cascade laser, including a quantum cascade laser, a high-precision current source, a constant temperature control device, a dual-beam modulation system, a beam collimator, a beam splitter, a Fourier Leaf infrared spectrometer, beam focuser, high frequency infrared detector, high precision oscilloscope. In the invention, the frequency modulation light source is used to irradiate the exit end face of the quantum cascade laser to realize high-speed amplitude and frequency modulation, and the amplitude modulation is positive modulation; Negative modulation: use frequency modulation light source and amplitude modulation to suppress the synchronization of the light source, realize the synchronous suppression of amplitude modulation, and realize pure frequency modulation.

Description

An all-optical pure frequency modulation system based on quantum cascade lasers

technical field

The invention relates to the fields of free space infrared optical communication technology and infrared laser spectrum technology, in particular to an all-optical pure frequency modulation system based on quantum cascade lasers.

Background technique

In the prior art, as a widely used infrared coherent light source, the quantum cascade laser has the advantages of narrow line width, high power, and can work at room temperature. Due to the low transmission loss of the mid-infrared laser in the atmosphere, it has the application advantages of free space optical communication; since the mid-infrared band covers the fingerprint spectral region of most gas molecules, it has great potential for trace gas detection. Advantage. Frequency modulation technology can increase the transmission bandwidth of quantum cascade lasers and the signal-to-noise ratio of spectral signals, but frequency modulation must be accompanied by amplitude modulation, which affects the accuracy of the signal, so suppressing amplitude modulation and realizing pure frequency modulation is have important application value.

Although it has been reported to realize pure frequency modulation of quantum cascade lasers by combining light and electricity, the way of electric modulation is affected by parasitic capacitance, the modulation speed is limited, and high-speed modulation cannot be achieved, and the way of combining light and electricity Due to the thermal effect of the laser current, the output wavelength of the quantum cascade laser is red-shifted, which reduces the amount of laser frequency variation caused by light modulation, and greatly limits the development of infrared laser spectroscopy and free space infrared optical communication technology.

Contents of the invention

The purpose of the present invention is to provide an all-optical pure frequency modulation system based on quantum cascade lasers, which solves the problem that the electrical modulation is affected by parasitic capacitance, the modulation speed is limited, and the combination of light and electricity is affected by the thermal effect of the laser current, so that The output wavelength of the quantum cascade laser is red-shifted, which reduces the problem of the amount of laser frequency variation caused by light modulation.

The present invention realizes through following technical scheme:

An all-optical pure frequency modulation system based on a quantum cascade laser, characterized in that it includes a quantum cascade laser, a high-precision current source, a constant temperature control device, a dual-beam modulation system, a beam collimator, a beam splitter, a Fourier Infrared spectrometer, beam focuser, high-frequency infrared detector, high-precision oscilloscope, including:

Quantum cascade lasers: used to generate visible or near-infrared light;

High-precision current source: used to provide DC or a current pulse sequence with pulse width Tp and repetition frequency ωr to the quantum cascade laser, so that the quantum cascade laser works in DC or pulse mode;

Constant temperature control device: used to provide a constant temperature working environment for the quantum cascade laser to ensure the stable operation of the quantum cascade laser;

Dual-beam modulation system: It is used to perform two modulations on the light output by the quantum cascade laser, one of which increases the modulation and the other decreases the modulation, and makes the amplitude of the output light wavelength oscillation proportional to the intensity of the visible light or near-infrared beam. Proportional, realize the amplitude, frequency modulation and amplitude suppression of quantum cascade lasers, realize pure frequency modulation, and output modulated light waves;

Beam collimator: collimate and adjust the light wave output by the quantum cascade laser and output it to the beam splitter;

Beam splitter: split the light wave output by the beam collimator into two beams with the same power, one of which is coupled into the Fourier transform infrared spectrometer, and the other beam is focused on the detection surface of the high-frequency infrared detector by the beam focuser superior;

Fourier transform infrared spectrometer: used to measure the wavelength change of the infrared light output by the quantum cascade laser;

High-frequency infrared detector: convert the detected optical signal into an electrical signal and transmit it to a high-precision oscilloscope, and the high-precision oscilloscope realizes the display of the signal.

The quantum cascade laser of the present invention can be a Fabry-Perot type quantum cascade laser, or a distributed feedback quantum cascade laser, and a high-precision current source provides a direct current or a pulse width of T _p to the quantum cascade laser. A current pulse sequence with a repetition rate of ω _r makes the quantum cascade laser work in a direct current or pulse mode; a constant temperature working environment is provided for the quantum cascade laser through a constant temperature device to ensure the stable operation of the quantum cascade laser. The dual-beam modulation system modulates the light output by the quantum cascade laser, so that the amplitude of the wavelength oscillation of the output light of the quantum cascade laser is proportional to the intensity of the visible light or near-infrared beam, realizing the amplitude, frequency modulation, and Amplitude suppression to achieve pure frequency modulation. After the modulated light wave passes through the beam collimator and beam splitter, it is divided into two beams with the same power, one of which is coupled into the Fourier transform infrared spectrometer, and the other beam is focused by the beam The detector is focused on the detection surface of the high-frequency infrared detector. The high-frequency infrared detector converts the detected optical signal into an electrical signal and transmits it to a high-precision oscilloscope. The high-precision oscilloscope realizes the display of the signal, and the high-precision current source Do synchronous triggering, and the finally obtained signal can be transmitted to the computer for real-time analysis, processing, and storage. After the double-beam modulation system of the present invention cooperates with the quantum cascade laser, it realizes pure frequency modulation. Compared with the photoelectric hybrid in the prior art In terms of modulation mode, its modulation speed is greatly improved without being affected by parasitic capacitance, and it is also not affected by the thermal effect of laser current, which solves the problem of red shift of quantum cascade laser output wavelength and reduces the laser frequency change caused by optical modulation quantity.

Specifically, the dual-beam modulation system includes a frequency modulation light source, an amplitude modulation suppression light source, multiple synchronous output semiconductor laser drivers, a first beam collimator, a first beam focuser, and a second beam collimator, a second beam focuser, wherein:

Multi-channel synchronous output semiconductor laser drive: used to provide DC with amplitude a or current pulse sequence with repetition frequency ω _m , so that the frequency modulated light source works in DC or pulse mode; at the same time provide DC or repetitive current with amplitude b a current pulse sequence with a frequency of ω _m , and is synchronized with the driving current of the frequency modulated light source, so that the amplitude modulation suppressed light source works in a DC or pulse mode;

Frequency modulation light source: As a visible or near-infrared laser light source, it generates a visible or near-infrared beam with a center wavelength of _λ1 , and focuses the visible or near-infrared beam on the quantum after passing through the first beam collimator and the first beam focuser The output end face of the cascade laser causes the infrared light wave output by the quantum cascade laser to oscillate at a frequency ω _m , and the amplitude increases, and the amplitude of the output light wavelength oscillation is proportional to the intensity of the visible light or near-infrared beam;

Amplitude modulation suppression light source: As a visible or near-infrared laser light source, a visible or near-infrared beam with a central wavelength of λ ₂ is generated, where λ ₁ >λ ₂ , and after passing through the second beam collimator and the second beam focuser, the The visible or near-infrared beam is focused on the exit end face of the quantum cascade laser, causing the infrared light wave output by the quantum cascade laser to oscillate at the frequency _ωm , and the amplitude decreases. Proportional.

The core of the present invention is a dual-beam modulation system, the central wavelength of the frequency modulation light source is λ ₁ ; through the drive of multiple synchronous output semiconductor lasers, a direct current with an amplitude of a or a current pulse sequence with a repetition frequency of ω _m is provided, so that the frequency modulation light source Work in DC or pulse mode; and focus the visible or near-infrared beam on the exit end face of the quantum cascade laser through the first beam collimator and the first beam focuser, causing the infrared light wave output by the quantum cascade laser to be at a frequency ω _m oscillation, and the amplitude increases, the amplitude of the output light wavelength oscillation is proportional to the intensity of the visible light or near-infrared beam, so as to realize the amplitude and frequency modulation of the distributed feedback quantum cascade laser; the center wavelength of the amplitude modulation suppression light source is λ ₂ , where λ ₁ >λ ₂ ; drive multiple synchronous output semiconductor lasers to provide a DC with amplitude b or a current pulse sequence with a repetition frequency ω _m , and ensure that it is synchronized with the drive current of the frequency-modulated light source, so that the amplitude modulation Inhibit the light source to work in DC or pulse mode; and focus the visible or near-infrared beam on the exit end face of the quantum cascade laser through the second beam collimator and the second beam focuser, causing the infrared light wave output by the quantum cascade laser to be The frequency ω _m oscillates, and the amplitude decreases, and the amplitude of the output light wavelength oscillation is proportional to the intensity of the visible light or near-infrared beam, so as to realize the amplitude suppression of the distributed feedback quantum cascade laser and realize pure frequency modulation; frequency modulation light source, Amplitude modulation suppresses the synchronization of visible or near-infrared light output by the light source, both of which are driven by DC or current pulse sequences with different amplitudes, the same phase, and a repetition frequency of ω _m driven by multiple synchronous output semiconductor lasers, so that by The positive amplitude modulation of the quantum cascade laser output infrared light caused by the frequency modulation light source is simultaneously offset by the negative amplitude modulation of the quantum cascade laser output infrared light caused by the amplitude modulation suppressing light source, and pure frequency modulation is realized.

The visible or near-infrared light emitted by the frequency-modulated light source has a photon energy corresponding to the bandgap energy of the top of the valence band and the upper energy level of the conduction band laser in the quantum cascade laser, or the difference is not more than 1 phonon energy; The amplitude modulation suppresses the visible or near-infrared light emitted by the light source, and its corresponding photon energy is greater than the bandgap energy of the top of the valence band and the upper energy level of the conduction band laser in the quantum cascade laser. Specifically, in order to better realize the purpose of the present invention, after different experiments and theoretical verifications have been carried out on the light wave energy of the dual-beam modulation system, the best implementation scheme has been found: using the visible or nearly Infrared light, whose corresponding photon energy is close to the bandgap energy of the semiconductor material with a smaller bandgap in the quantum cascade laser, through photoinduced excitation makes the electrons inside the resonator of the quantum cascade laser jump from the valence band to the upper energy level of the conduction band laser , which increases the number of electrons on the energy level of the conduction band laser, increases the laser gain, and realizes the positive amplitude modulation of the quantum cascade laser. At the same time, the increase in the number of electrons on the energy level of the conduction band laser will change the quantum The refractive index of the resonant cavity of the cascade laser changes the effective cavity length of the resonant cavity of the quantum cascade laser, thereby changing the output infrared wavelength or frequency of the quantum cascade laser, and realizing the frequency modulation of the quantum cascade laser; amplitude modulation Suppress the visible or near-infrared light emitted by the light source, and the corresponding photon energy is much larger than the bandgap energy of the semiconductor material with a smaller bandgap in the quantum cascade laser. Jumping to the conduction band, the high energy makes the electrons not only jump to the upper energy level of the laser, but also the energy level of higher energy and the high-k state of the energy level. In a short time, the electrons pass through electron-electron scattering, electron- The energy is released in the way of phonon scattering, most of the energy will increase the electron temperature in the form of thermal energy, and the increase of the electron temperature will increase the threshold current of the quantum cascade laser, thereby reducing the infrared light output power of the quantum cascade laser, realizing the negative The amplitude modulation and the change of the electronic distribution of the conduction band energy level will change the refraction index of the resonant cavity of the quantum cascade laser, thereby changing the effective cavity length of the resonant cavity of the quantum cascade laser, and then changing the infrared output of the quantum cascade laser The wavelength or frequency realizes the frequency modulation of the quantum cascade laser, so when the negative amplitude modulation is the same as the positive amplitude modulation, pure frequency modulation is realized.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention is an all-optical pure frequency modulation system based on quantum cascade lasers, which modulates the light output by quantum cascade lasers through a dual-beam modulation system, so that the amplitude of the wavelength oscillation of the output light of quantum cascade lasers is comparable to that of visible light or The intensity of the near-infrared beam is proportional to the amplitude, frequency modulation, and amplitude suppression of the quantum cascade laser, and pure frequency modulation is realized. After the modulated light wave passes through the beam collimator and beam splitter, it is divided into two beams with the same power , one of which is coupled into the Fourier infrared spectrometer, and the other beam is focused on the detection surface of the high-frequency infrared detector through the beam focuser, and the high-frequency infrared detector converts the detected optical signal into an electrical signal for transmission For a high-precision oscilloscope, the display of the signal is realized by the high-precision oscilloscope, and the high-precision current source is used for synchronous triggering. The finally obtained signal can be transmitted to the computer for real-time analysis, processing, and storage. The dual-beam modulation system of the present invention is compatible with quantum-level After the laser is combined, the pure frequency modulation is realized. Compared with the photoelectric hybrid modulation method in the prior art, the modulation speed is greatly improved without being affected by the parasitic capacitance, and is not affected by the thermal effect of the laser current. The red shift of output wavelength of cascaded lasers reduces the laser frequency variation caused by light modulation;

2. An all-optical pure frequency modulation system based on the quantum cascade laser of the present invention adopts a synchronous amplitude modulation to suppress the light source, and the photon energy corresponding to the direct current or intensity changes at a high speed and the wavelength is much greater than that in the quantum cascade laser Visible or near-infrared laser beams with the bandgap energy of a semiconductor material with a small bandgap are converged on the exit end face of the quantum cascade laser through a focusing device, so that they can excite the valence band electrons to the conduction band of the laser in the quantum cascade laser cavity On the upper energy level of the laser or the energy level with higher energy and the high-k state, the temperature of the conduction band electrons is increased by means of electron-electron flashing and electron-phonon scattering, thereby increasing the threshold current of the quantum cascade laser and realizing negative amplitude At the same time, due to the change of the electron concentration in the conduction band, the equivalent refractive index of the quantum cascade laser produces a high-speed periodic oscillation, which leads to a high-speed periodic oscillation of the output wavelength. When the negative amplitude modulation is the same as the positive amplitude modulation , the amplitude modulation is completely suppressed, realizing pure frequency modulation;

3. An all-optical pure frequency modulation system based on quantum cascade lasers of the present invention uses a frequency modulated light source to irradiate the exit end face of quantum cascade lasers to achieve high-speed amplitude and frequency modulation, and the amplitude modulation is positive modulation; amplitude modulation is used to suppress light source irradiation The output end face of the quantum cascade laser realizes high-speed amplitude and frequency modulation, and the amplitude modulation is negative modulation; the frequency modulation light source and the amplitude modulation are used to suppress the synchronization of the light source, and the synchronization suppression of the amplitude modulation is realized, and the pure frequency modulation is realized; the signal is analyzed and processed in real time 1. Storage is to realize the conversion of pure frequency modulation optical signal of quantum cascade laser and the detection of amplitude modulation/frequency modulation through the signal acquisition part, so as to realize real-time analysis, processing and storage.

Description of drawings

The drawings described here are used to provide a further understanding of the embodiments of the present invention, constitute a part of the application, and do not limit the embodiments of the present invention. In the attached picture:

Fig. 1 is a schematic diagram of the principle framework of the present invention;

Fig. 2 is the position schematic diagram of optical path of the present invention;

Fig. 3 is a light wave energy level diagram of the frequency modulation light source and the amplitude modulation suppression light source of the present invention;

Fig. 4 is the pulse intensity waveform diagram when the quantum cascade laser of the present invention is not modulated;

Fig. 5 is a pulse intensity waveform chart of the modulated quantum cascade laser of the present invention.

Marks and corresponding parts names in the attached drawings:

1-quantum cascade laser, 2-frequency modulation light source, 3-amplitude modulation suppression light source, 4-high-precision current source, 5-constant temperature control device, 6-multi-channel synchronous output semiconductor laser drive, 7-first beam collimation Device, 8-first beam focuser, 9-second beam collimator, 10-second beam focuser, 11-beam collimator, 12-beam splitter, 13-Fourier transform infrared spectrometer, 14- Beam focuser, 15-high-frequency infrared detector, 16-high-precision oscilloscope, 17-computer.

Detailed ways

In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples. The schematic embodiments of the present invention and their descriptions are only used to explain the present invention, and are not intended as an explanation of the present invention. limited.

Example

As shown in Figure 1, the present invention is an all-optical pure frequency modulation system based on quantum cascade laser, including quantum cascade laser 1, frequency modulation light source 2, amplitude modulation suppression light source 3, high-precision current source 4, constant temperature control device 5. Multi-channel synchronous output semiconductor laser driver 6, first beam collimator 7, first beam focuser 8, second beam collimator 9, second beam focuser 10, beam collimator 11, beam splitter 12. Fourier transform infrared spectrometer 13, beam focuser 14, high-frequency infrared detector 15, high-precision oscilloscope 16, computer 17, wherein: as shown in Figure 2, the quantum cascade laser 1 is fixed on the metal heat sink, the frequency Modulation of visible light or near-infrared laser beams and amplitude modulation inhibit visible light or near-infrared laser beams from being converged on the exit end face of quantum cascade lasers, causing high-speed frequency modulation of quantum cascade lasers, while suppressing amplitude modulation, thereby realizing quantum cascade lasers All-optical pure frequency modulation, high-precision current source 4 provides DC or current pulse sequence with pulse width T _p and repetition frequency ω _r to quantum cascade laser 1, so that quantum cascade laser 1 works in DC or pulse mode Provide a constant temperature working environment for the quantum cascade laser 1 through the constant temperature device 5 to ensure the stable operation of the quantum cascade laser 1, and the multi-channel synchronous output semiconductor laser drive 6 provides a direct current with an amplitude of a or a repetition rate of ω _m The current pulse sequence makes the frequency modulation light source 2 work in DC or pulse mode; at the same time, the multi-channel synchronous output semiconductor laser driver 6 provides a DC with an amplitude of b or a current pulse sequence with a repetition frequency of ω _m , and is compatible with the frequency modulation light source The driving current of 2 keeps synchronously, makes amplitude modulation suppression light source 3 work under direct current _or pulse mode; A beam collimator 7 and a first beam focuser 8 focus the visible or near-infrared beam on the exit end face of the quantum cascade laser 1, causing the infrared light wave output by the quantum cascade laser 1 to oscillate at a frequency _ωm , and the amplitude increases Large, the amplitude of the output light wavelength oscillation is proportional to the intensity of the visible light or near-infrared beam, the visible or near-infrared light emitted by the frequency modulation light source 2, the corresponding photon energy is close to that of the smaller band gap in the quantum cascade laser The bandgap energy of the semiconductor material, through photoinduced excitation, makes the electrons inside the quantum cascade laser resonator jump from the valence band to the upper energy level of the conduction band laser, thereby increasing the number of electrons on the upper energy level of the conduction band laser and increasing the laser gain. The positive amplitude modulation of the quantum cascade laser is realized. At the same time, the increase in the number of energy-level electrons on the conduction band laser will change the refraction index of the quantum cascade laser resonator, thereby changing the resonant cavity of the quantum cascade laser. The effective cavity length, and then changed the quantum cascade laser output infrared wavelength or frequency, realized the frequency modulation to the quantum cascade laser; the amplitude modulation suppression light source 3 is a visible or near-infrared laser light source, and the visible light source with a central wavelength of λ ₂ is produced. or near-infrared beam, wherein λ ₁ >λ ₂ , and after passing through the second beam collimator 9 and the second beam focuser 10, the visible or near-infrared beam is focused on the exit end face of the quantum cascade laser 11, causing quantum cascade The infrared light wave output by the laser 1 oscillates at a frequency _ωm , and the amplitude decreases. The amplitude of the output light wavelength oscillation is proportional to the intensity of the visible light or near-infrared beam, and the amplitude modulation suppresses the visible or near-infrared light emitted by the light source. The corresponding The photon energy of the quantum cascade laser is much larger than the bandgap energy of the semiconductor material with a smaller bandgap in the quantum cascade laser. Through photoexcitation, the electrons inside the quantum cascade laser resonator transition from the valence band to the conduction band. Excessive energy makes the electrons not only transition Up to the upper energy level of the laser, including higher energy levels and their high-k states, in a short period of time, electrons release energy through electron-electron scattering and electron-phonon scattering, and most of the energy will be in the form of Thermal energy increases the electron temperature, and the increase in electron temperature will increase the threshold current of the quantum cascade laser, thereby reducing the infrared light output power of the quantum cascade laser, realizing negative amplitude modulation, and at the same time changing the electron distribution of the conduction band energy level The refractive index of the resonant cavity of the quantum cascade laser will be changed, thereby changing the effective cavity length of the resonant cavity of the quantum cascade laser, and then changing the output infrared wavelength or frequency of the quantum cascade laser, realizing the frequency of the quantum cascade laser Modulation, so when the magnitude of the negative amplitude modulation is the same as that of the positive amplitude modulation, pure frequency modulation is realized, as shown in Figure 3, as shown in the left figure, the visible or near-infrared light emitted by the frequency modulation light source 2, its corresponding photon The energy is close to the bandgap energy of the semiconductor material with the smaller bandgap in quantum cascade laser 1. Through photo-induced excitation, the electrons inside the quantum cascade laser resonator transition from the valence band to the upper energy level of the conduction band laser, thereby increasing the conduction band The number of electrons on the energy level of the laser increases the laser gain and realizes the positive amplitude modulation of the quantum cascade laser. At the same time, the increase in the number of electrons on the energy level of the conduction band laser will change the resonant cavity of the quantum cascade laser. Refractive index, thus changing the effective cavity length of the resonant cavity of the quantum cascade laser, and then changing the output infrared wavelength or frequency of the quantum cascade laser, realizing the frequency modulation of the quantum cascade laser; as shown in the right figure, the amplitude modulation suppresses The visible or near-infrared light emitted by the light source 3 has a corresponding photon energy that is much greater than the bandgap energy of the semiconductor material with a smaller bandgap in the quantum cascade laser 1. Through photoexcitation, the electrons inside the quantum cascade laser resonator are valence The band jumps to the conduction band, and the high energy makes the electrons not only jump to the upper energy level of the laser, but also include higher energy levels and their high-k states. In a short time, the electrons pass through electron-electron scattering, and the electrons -The energy is released in the way of phonon scattering, most of the energy will increase the electron temperature in the form of thermal energy, and the increase of the electron temperature will increase the threshold current of the quantum cascade laser, thereby reducing the infrared light output power of the quantum cascade laser, realizing the Negative amplitude modulation, and at the same time, the change of the electronic distribution of the conduction band energy level will change the refraction index of the quantum cascade laser resonator, thereby changing the effective cavity length of the resonant cavity of the quantum cascade laser, and then changing the output of the quantum cascade laser The infrared wavelength or frequency realizes the frequency modulation of the quantum cascade laser, so when the magnitude of the negative amplitude modulation and the positive amplitude modulation are the same, the pure frequency modulation is realized; the pure frequency modulation infrared light of the quantum cascade laser 1 passes through the beam quasi Straightener 11 is divided into two beams of light by beam splitter 12, one beam enters in Fourier transform spectrometer 13, is used for measuring its wavelength variation; The detection surface is used to measure the amplitude variation; the high-precision oscilloscope 16 and the computer 17 are used to realize real-time display, analysis, processing and storage of signals.

As shown in Figure 4, when the quantum cascade laser is not modulated, the amplitude of the infrared light it outputs is shown by the dotted line; when only frequency-modulated visible or near-infrared light is focused on the exit end of the quantum cascade laser, the infrared light it outputs The amplitude increases, as shown by the solid line; when the amplitude modulation suppresses visible or near-infrared light from focusing on the exit facet of the quantum cascade laser, the amplitude of its output infrared light is suppressed, as shown by the dotted line.

As shown in Figure 5, when the quantum cascade laser is not modulated, the central wavelength position of the infrared light it outputs is shown by the solid line; when only the frequency modulated visible or near-infrared light is focused on the exit end of the quantum cascade laser, its output The position of the central wavelength of the infrared light is blue-shifted, as shown by the dotted line; when only the amplitude modulation suppresses the visible or near-infrared light to focus on the exit end face of the quantum cascade laser, the position of the central wavelength of the infrared light it outputs is blue-shifted, as indicated by the dotted line It shows that when two beams of visible or near-infrared light are focused on the exit facet of the quantum cascade laser at the same time, the blue shift of the central wavelength position of the output infrared light increases, which is basically the same as the sum of the blue shifts caused by the two beams of light respectively, as shown in Broken dotted lines show.

The quantum cascade laser all-optical pure frequency modulation system provided by the invention can be applied to high-sensitivity infrared laser spectrum technology and high-precision free-space frequency modulation infrared optical communication.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (3)

1. An all-optical pure frequency modulation system based on a quantum cascade laser, characterized in that it includes a quantum cascade laser (1), a high-precision current source (4), a constant temperature control device (5), a dual-beam modulation system, and a beam Collimator (11), beam splitter (12), Fourier transform infrared spectrometer (13), beam focuser (14), high-frequency infrared detector (15), high-precision oscilloscope (16), of which: Quantum cascade laser (1): used to generate visible light or near-infrared light, the quantum cascade laser (1) is fixed on a metal heat sink, the frequency modulates the visible or near-infrared laser beam and the amplitude modulation suppresses the visible or near-infrared laser beam from being converging on the exit end face of the quantum cascade laser (1); High-precision current source (4): used to provide DC or a current pulse sequence with pulse width Tp and repetition frequency ωr to the quantum cascade laser (1), so that the quantum cascade laser (1) works in DC or pulse mode ; Constant temperature control device (5): used to provide a constant temperature working environment for the quantum cascade laser (1) to ensure the stable operation of the quantum cascade laser (1); Dual-beam modulation system: used to perform two modulations on the light output by the quantum cascade laser (1), one of which increases the modulation and the other decreases the modulation, and makes the amplitude of the output light wavelength oscillation comparable to that of visible light or near-infrared beams The light intensity is proportional to realize the amplitude, frequency modulation and amplitude suppression of the quantum cascade laser (1), realize pure frequency modulation, and output the modulated light wave; Beam collimator (11): collimate and adjust the light wave output by the quantum cascade laser (1) and output it to the beam splitter (12); Beam splitter (12): Split the light wave output by the beam collimator (11) into two beams with the same power, one of which is coupled into the Fourier transform infrared spectrometer (13), and the other beam passes through the beam focuser ( 14) focus on the detection surface of the high-frequency infrared detector (15); Fourier transform infrared spectrometer (13): used to measure the wavelength change of the infrared light output by the quantum cascade laser (1); High-frequency infrared detector (15): Convert the detected optical signal into an electrical signal and transmit it to the high-precision oscilloscope (16), and the high-precision oscilloscope (16) realizes the display of the signal. 2. An all-optical pure frequency modulation system based on quantum cascade lasers according to claim 1, characterized in that: the dual-beam modulation system includes a frequency modulation light source (2), an amplitude modulation suppression light source (3) , multiple synchronous output semiconductor laser drive (6), first beam collimator (7), first beam focuser (8), and second beam collimator (9), second beam focuser (10) ,in: Multi-channel synchronous output semiconductor laser drive (6): used to provide DC with amplitude a or current pulse sequence with repetition frequency ω _m , so that the frequency modulated light source (2) works in DC or pulse mode; at the same time provide amplitude b is a direct current or a current pulse sequence with a repetition frequency of ω _m , and is synchronized with the driving current of the frequency modulation light source (2), so that the amplitude modulation suppression light source (3) works in a direct current or pulse mode; Frequency modulation light source (2): As a visible or near-infrared laser light source, it generates a visible or near-infrared beam with a center wavelength of λ ₁ , and passes through the first beam collimator (7) and the first beam focuser (8) Focusing the visible or near-infrared beam on the exit end face of the quantum cascade laser (1), causing the infrared light wave output by the quantum cascade laser (1) to oscillate at a frequency ω _m , and the amplitude increases, and the amplitude of the output light wavelength oscillation is the same as Visible light or near-infrared beam intensity is proportional; Amplitude modulation suppression light source (3): As a visible or near-infrared laser light source, it generates a visible or near-infrared beam with a central wavelength of λ ₂ , where λ ₁ > λ ₂ , and passes through the second beam collimator (9) and the first The two-beam focuser (10) focuses the visible or near-infrared beam on the exit end face of the quantum cascade laser (1), causing the infrared light wave output by the quantum cascade laser (1) to oscillate at a frequency ω _m , and the amplitude decreases, The amplitude of the wavelength oscillation of the output light is directly proportional to the intensity of the visible or near-infrared beam. 3. An all-optical pure frequency modulation system based on quantum cascade lasers according to claim 2, characterized in that: the visible or near-infrared light emitted by the frequency modulation light source (2) has a corresponding photon energy The bandgap energy of the top of the valence band and the upper energy level of the conduction band laser in the quantum cascade laser (1) is equal to or differs by no more than 1 phonon energy; the amplitude modulation suppresses the visible or near-infrared light emitted by the light source (3), The corresponding photon energy is greater than the bandgap energy of the top of the valence band and the upper energy level of the conduction band laser in the quantum cascade laser (1).

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