CN106936070B - All-optical pure frequency modulation system based on quantum cascade laser - Google Patents
All-optical pure frequency modulation system based on quantum cascade laser Download PDFInfo
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- CN106936070B CN106936070B CN201710330645.5A CN201710330645A CN106936070B CN 106936070 B CN106936070 B CN 106936070B CN 201710330645 A CN201710330645 A CN 201710330645A CN 106936070 B CN106936070 B CN 106936070B
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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
- H01S5/00—Semiconductor lasers
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- H01S5/042—Electrical excitation ; Circuits therefor
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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
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/024—Arrangements for thermal management
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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
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
- H01S5/0608—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by light, e.g. optical switch
Abstract
The invention discloses an all-optical pure frequency modulation system based on a quantum cascade laser, which comprises the quantum cascade laser, a high-precision current source, a constant temperature control device, a double-beam modulation system, a beam collimator, a beam splitter, a Fourier infrared spectrometer, a beam focusing device, a high-frequency infrared detector and a high-precision oscilloscope. The invention utilizes the frequency modulation light source to irradiate the emergent end face of the quantum cascade laser to realize high-speed amplitude and frequency modulation, and the amplitude modulation is positive modulation; the amplitude modulation is utilized to inhibit the light source from irradiating the emergent end face of the quantum cascade laser to realize high-speed amplitude and frequency modulation, and the amplitude modulation is negative modulation; the synchronization of the frequency modulation light source and the amplitude modulation suppression light source is utilized to realize the synchronization suppression of the amplitude modulation and realize the pure frequency modulation.
Description
Technical Field
The invention relates to the technical fields of free space infrared light communication technology and infrared laser spectrum, in particular to an all-optical pure frequency modulation system based on a quantum cascade laser.
Background
In the prior art, the quantum cascade laser is used as a widely used infrared coherent light source, and has the advantages of narrow line width, high power, capability of working in room temperature environment and the like. The mid-infrared laser has the application advantage of free space optical communication because of low transmission loss in the atmosphere; the mid-infrared band is of great advantage for trace gas detection, since it covers the fingerprint spectrum of most gas molecules. The frequency modulation technology can increase the transmission bandwidth of the quantum cascade laser and the signal-to-noise ratio of the spectrum signal, but the frequency modulation is necessarily accompanied with the amplitude modulation, and the amplitude modulation influences the accuracy of the signal, so that the amplitude modulation is restrained, and the realization of pure frequency modulation is important in application value.
Although the pure frequency modulation of the quantum cascade laser is realized by adopting an optical and electric combination mode, the electric modulation mode is influenced by parasitic capacitance, the modulation speed is limited, high-speed modulation cannot be realized, and the optical and electric combination mode is subjected to the current thermal effect of the laser, so that the output wavelength of the quantum cascade laser is red shifted, the laser frequency variation caused by optical modulation is reduced, and the development of an infrared laser spectrum technology and a free space infrared communication technology is greatly limited.
Disclosure of Invention
The invention aims to provide an all-optical pure frequency modulation system based on a quantum cascade laser, which solves the problems that an electric modulation mode is influenced by parasitic capacitance, the modulation speed is limited, and an optical and electric combination mode is influenced by the current thermal effect of the laser, so that the output wavelength of the quantum cascade laser is red shifted, and the laser frequency variation caused by optical modulation is reduced.
The invention is realized by the following technical scheme:
all-optical pure frequency modulation system based on quantum cascade laser, characterized by including quantum cascade laser, high accuracy current source, constant temperature control device, two light beam modulation system, beam collimator, beam splitter, fourier infrared spectrometer, beam focus ware, high frequency infrared detector, high accuracy oscilloscope, wherein:
quantum cascade laser: for generating visible or near infrared light;
high precision current source: the method comprises the steps of providing a direct current or a current pulse sequence with a pulse width Tp and a repetition frequency omega r for the quantum cascade laser, so that the quantum cascade laser works in a direct current or pulse mode;
constant temperature control device: the method is used for providing a constant-temperature working environment for the quantum cascade laser and ensuring the stable operation of the quantum cascade laser;
dual beam modulation system: the device is used for carrying out two kinds of modulation on light output by the quantum cascade laser, wherein one kind of modulation is increased, the other kind of modulation is reduced, the amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light beam, the amplitude, the frequency modulation and the amplitude inhibition of the quantum cascade laser are realized, the pure frequency modulation is realized, and the modulated light wave is output;
beam collimator: performing collimation adjustment on light waves output by the quantum cascade laser and outputting the light waves to a beam splitter;
a beam splitter: dividing the light wave output by the beam collimator into two beams with the same power, wherein one beam is coupled into a Fourier infrared spectrometer, and the other beam is focused on a detection surface of a high-frequency infrared detector through a beam focusing device;
fourier infrared spectrometer: the device is used for measuring the wavelength change of the infrared light output by the quantum cascade laser;
high-frequency infrared detector: the detected optical signals are converted into electric signals and transmitted to a high-precision oscilloscope, and the high-precision oscilloscope realizes the display of the signals.
The quantum cascade laser of the invention can be a Fabry-Perot quantum cascade laser, and also can be a distributed feedback quantum cascade laser, and direct current or pulse width T is provided for the quantum cascade laser through a high-precision current source p At a repetition frequency of omega r The quantum cascade laser is enabled to work in a direct current or pulse mode; the constant temperature device provides a constant temperature working environment for the quantum cascade laser, the stable working of the quantum cascade laser is ensured, the light output by the quantum cascade laser is modulated through the double-beam modulation system, so that the amplitude of the light wavelength oscillation output by the quantum cascade laser is in direct proportion to the light intensity of the visible light or near infrared light beam, the amplitude, the frequency modulation and the amplitude inhibition of the quantum cascade laser are realized, the pure frequency modulation is realized, the modulated light wave is divided into two beams with the same power after passing through the beam collimator and the beam splitter, one beam is coupled into the Fourier infrared spectrometer, the other beam is focused on the detection surface of the high-frequency infrared detector through the beam focusing device, and the high-frequency infrared detection is realizedThe dual-beam modulation system is matched with the quantum cascade laser to realize pure frequency modulation, and compared with the photoelectric hybrid modulation mode in the prior art, the speed of modulation is greatly improved without being influenced by parasitic capacitance and without being influenced by the current thermal effect of the laser, the problem of red shift of the output wavelength of the quantum cascade laser is solved, and the laser frequency variation caused by light modulation is reduced.
Specifically, the dual-beam modulation system includes a frequency modulated light source, an amplitude modulated suppressed light source, a multiplexed output semiconductor laser drive, a first beam collimator, a first beam focuser, and a second beam collimator, a second beam focuser, wherein:
multiplex synchronous output semiconductor laser drive: for providing a direct current of amplitude a or a repetition frequency omega m The current pulse sequence of (2) enabling the frequency modulated light source to operate in a direct current or pulse mode; at the same time providing a DC of amplitude b or a repetition frequency omega m The current pulse sequence of the frequency modulation light source is kept synchronous with the driving current of the frequency modulation light source, so that the amplitude modulation inhibition light source works in a direct current or pulse mode;
a frequency modulated light source: as a visible or near infrared laser source, a central wavelength lambda is generated 1 After passing through the first beam collimator and the first beam focusing device, the visible or near-infrared beam is focused on the emergent end face of the quantum cascade laser, so that the infrared light wave output by the quantum cascade laser is caused to have a frequency omega m The amplitude of the oscillation is proportional to the light intensity of the visible light or the near infrared light;
amplitude modulation suppressing light source: as a visible or near infrared laser source, a central wavelength lambda is generated 2 Wherein lambda is the visible or near infrared beam of 1 >λ 2 And pass through the firstAfter the two-beam collimator and the second beam focusing device, the visible or near-infrared beam is focused on the emergent end face of the quantum cascade laser, so that the infrared light wave output by the quantum cascade laser is caused to have the frequency omega m The amplitude of the oscillation is proportional to the intensity of the visible or near infrared light beam.
The core of the invention is a double-beam modulation system, the central wavelength of the frequency modulation light source is lambda 1 The method comprises the steps of carrying out a first treatment on the surface of the Providing DC with amplitude a or repetition frequency omega by multiplexing synchronous output semiconductor laser drive m The current pulse sequence of (2) enabling the frequency modulated light source to operate in a direct current or pulse mode; and the visible or near infrared light beam is focused on the emergent end face of the quantum cascade laser through the first beam collimator and the first beam focusing device, so that the infrared light wave output by the quantum cascade laser is caused to have the frequency omega m The amplitude of the oscillation is increased, and the amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light beam, so that the amplitude and frequency modulation of the distributed feedback type quantum cascade laser is realized; the center wavelength of the amplitude modulation suppressing light source is lambda 2 Wherein lambda is 1 >λ 2 The method comprises the steps of carrying out a first treatment on the surface of the Providing DC with amplitude b or repetition frequency omega by multiplexing synchronous output semiconductor laser drive m The current pulse sequence of the frequency modulation light source is ensured to keep synchronous with the driving current of the frequency modulation light source, so that the amplitude modulation inhibition light source works in a direct current or pulse mode; and focusing the visible or near infrared beam on the emergent end face of the quantum cascade laser through a second beam collimator and a second beam focusing device to cause the infrared light wave output by the quantum cascade laser to have a frequency omega m The amplitude of the oscillation is reduced, and the amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light beam, so that the amplitude suppression of the distributed feedback type quantum cascade laser is realized, and the pure frequency modulation is realized; the frequency modulation light source and the amplitude modulation suppression light source output visible light or near infrared light synchronously, and the two are provided by multiplexing synchronous output semiconductor laser drive and have different direct currents or amplitude values, same phase and omega repetition frequency m Is driven by a current pulse sequence such that the quantity caused by the frequency modulated light sourceThe positive amplitude modulation of the infrared light output by the sub-cascade laser is counteracted by the negative amplitude modulation of the infrared light output by the quantum cascade laser caused by the amplitude modulation inhibition light source, so that pure frequency modulation is realized.
The energy of photons corresponding to visible light or near infrared light emitted by the frequency modulation light source is equal to or different from the band gap energy of the energy levels on the valence band top and the conduction band laser in the quantum cascade laser by not more than 1 phonon energy; the amplitude modulation suppresses visible or near infrared light emitted by the light source, which corresponds to photon energy greater than band gap energy of energy levels on the valence band top and conduction band lasers in the quantum cascade laser. Specifically, in order to better achieve the purpose of the present invention, after performing different experiments and theoretical verification on the light wave energy of the dual-beam modulation system, the best implementation scheme is found: the method is characterized in that visible or near infrared light emitted by a frequency modulation light source is adopted, the corresponding photon energy is close to the band gap energy of a semiconductor material with smaller band gap in a quantum cascade laser, electrons in a resonant cavity of the quantum cascade laser are enabled to transit from a valence band to an upper energy level of conduction band laser through photoixcitation, the number of electrons on the upper energy level of the conduction band laser is further increased, the laser gain is increased, positive amplitude modulation of the quantum cascade laser is achieved, meanwhile, the number of electrons on the upper energy level of the conduction band laser is increased, the refractive index of the resonant cavity of the quantum cascade laser is changed, and therefore the effective cavity length of the resonant cavity of the quantum cascade laser is changed, the output infrared wavelength or frequency of the quantum cascade laser is further changed, and the frequency modulation of the quantum cascade laser is achieved; the amplitude modulation suppresses visible or near-infrared light emitted by a light source, the corresponding photon energy is far greater than the band gap energy of a semiconductor material with a smaller band gap in the quantum cascade laser, electrons in the resonant cavity of the quantum cascade laser are enabled to be transited from a valence band to a conduction band through photoexcitation, the electrons are enabled to be transited to the upper energy level of laser light, the energy level of the electrons and the high-k state of the energy level are included, in a short time, the electrons release energy in a mode of electron-electron scattering and electron-phonon scattering, most of the energy increases the electron temperature in a heat energy mode, the increase of the electron temperature increases the threshold current of the quantum cascade laser, the infrared light output power of the quantum cascade laser is further reduced, negative amplitude modulation is achieved, meanwhile, the refractive index of the resonant cavity of the quantum cascade laser is changed through change of the electron distribution of the energy level of the conduction band, the effective cavity length of the resonant cavity of the quantum cascade laser is further changed, the infrared wavelength or frequency of the quantum cascade laser is output, and the frequency modulation of the quantum cascade laser is achieved.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the invention relates to an all-optical pure frequency modulation system based on a quantum cascade laser, which modulates light output by the quantum cascade laser through a double-beam modulation system, so that the amplitude of optical wavelength oscillation output by the quantum cascade laser is in direct proportion to the light intensity of visible light or near infrared light, the amplitude, frequency modulation and amplitude inhibition of the quantum cascade laser are realized, pure frequency modulation is realized, the modulated light waves are divided into two beams with the same power after passing through a beam collimator and a beam splitter, one beam is coupled into a Fourier infrared spectrometer, the other beam is focused on a detection surface of a high-frequency infrared detector through a beam focusing device, the detected light signals are converted into electric signals by the high-frequency infrared detector and are transmitted to a high-precision oscilloscope, the display of the signals is realized by the high-precision oscilloscope, and the signals finally obtained by synchronous triggering by a high-precision current source can be transmitted to a computer for real-time analysis, processing and storage;
2. the invention relates to an all-optical pure frequency modulation system based on a quantum cascade laser, which adopts a synchronous amplitude modulation suppression light source, and by changing direct current or intensity at a high speed and periodically, photon energy corresponding to wavelength is far larger than band gap energy of a semiconductor material in the quantum cascade laser, visible light or near infrared light laser beams with smaller band gap energy are converged on an emergent end face of the quantum cascade laser through a focusing device, valence band electrons are excited to an upper energy level or a higher energy level and a high k state of laser conduction band laser in a resonant cavity of the quantum cascade laser, the temperature of conduction band electrons is increased in a mode of electron-electron flash and electron-phonon scattering, so that threshold current of the quantum cascade laser is increased, negative amplitude modulation is realized, and meanwhile, due to the change of electron concentration of the conduction band, the equivalent refractive index of the resonant cavity of the quantum cascade laser generates high-speed periodic oscillation, so that the high-speed periodic oscillation of output wavelength is caused, and when the negative amplitude modulation is the same as the positive amplitude modulation, the amplitude modulation is completely suppressed, and the pure frequency modulation is realized;
3. the invention relates to an all-optical pure frequency modulation system based on a quantum cascade laser, which utilizes a frequency modulation light source to irradiate the emergent end face of the quantum cascade laser to realize high-speed amplitude and frequency modulation, and the amplitude modulation is positive modulation; the amplitude modulation is utilized to inhibit the light source from irradiating the emergent end face of the quantum cascade laser to realize high-speed amplitude and frequency modulation, and the amplitude modulation is negative modulation; synchronization of the frequency modulation light source and the amplitude modulation suppression light source is utilized to realize synchronous suppression of the amplitude modulation and realize pure frequency modulation; the real-time analysis, processing and storage of the signals are realized by converting the pure frequency modulation optical signals of the quantum cascade laser and detecting the amplitude modulation/frequency modulation quantity through a signal acquisition part.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention. In the drawings:
FIG. 1 is a schematic diagram of a principal frame of the present invention;
FIG. 2 is a schematic view of the position of the optical path of the present invention;
FIG. 3 is a graph of the energy level of light waves of a frequency modulated light source and an amplitude modulated suppressed light source of the present invention;
FIG. 4 is a graph of pulse intensity waveforms for a quantum cascade laser of the present invention without modulation;
fig. 5 is a waveform diagram of pulse intensity after modulation of the quantum cascade laser of the present invention.
In the drawings, the reference numerals and corresponding part names:
the device comprises a 1-quantum cascade laser, a 2-frequency modulation light source, a 3-amplitude modulation suppression light source, a 4-high-precision current source, a 5-constant temperature control device, a 6-multi-channel synchronous output semiconductor laser driver, a 7-first beam collimator, an 8-first beam focusing device, a 9-second beam collimator, a 10-second beam focusing device, an 11-beam collimator, a 12-beam splitter, a 13-Fourier infrared spectrometer, a 14-beam focusing device, a 15-high-frequency infrared detector, a 16-high-precision oscilloscope and a 17-computer.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples, which are illustrative embodiments of the present invention and the description thereof are only for explaining the present invention and are not limiting the present invention.
Examples
As shown in fig. 1, the full-optical pure frequency modulation system based on the quantum cascade laser of the present invention includes a quantum cascade laser 1, a frequency modulation light source 2, an amplitude modulation suppression light source 3, a high-precision current source 4, a constant temperature control device 5, a multi-path synchronous output semiconductor laser driver 6, a first beam collimator 7, a first beam focuser 8, a second beam collimator 9, a second beam focuser 10, a beam collimator 11, a beam splitter 12, a fourier infrared spectrometer 13, a beam focuser 14, a high-frequency infrared detector 15, a high-precision oscilloscope 16, and a computer 17, wherein: as shown in fig. 2, the quantum cascade laser 1 is fixed on a metal heat sink, and frequency modulated visible light or near infrared laser beams and amplitude modulated suppression visible light or near infrared laser beams are converged on an emergent end face of the quantum cascade laser to cause high-speed frequency modulation of the quantum cascade laser, and simultaneously suppress amplitude modulation, thereby realizing full-optical pure frequency modulation of the quantum cascade laser and high-precision electricityThe current source 4 supplies direct current or pulse width T to the sub-cascade laser 1 p At a repetition frequency of omega r The quantum cascade laser 1 is operated in a direct current or pulse mode; the constant temperature device 5 provides a constant temperature working environment for the quantum cascade laser 1, ensures the stable operation of the quantum cascade laser 1, and the multi-channel synchronous output semiconductor laser driver 6 provides direct current with amplitude of a or has repetition frequency of omega m The frequency modulated light source 2 is made to operate in a direct current or pulse mode; the multiplexed synchronous output semiconductor laser driver 6 provides a DC with amplitude b or a repetition frequency omega m And is kept synchronous with the driving current of the frequency modulated light source 2, so that the amplitude modulation suppressing light source 3 operates in a direct current or pulse mode; the frequency modulation light source 2 is a visible or near infrared laser light source, and generates a center wavelength lambda 1 After passing through the first beam collimator 7 and the first beam focuser 8, the visible or near-infrared beam is focused on the emergent end face of the quantum cascade laser 1, so that the infrared light wave output by the quantum cascade laser 1 is caused to have a frequency omega m The amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light, the frequency modulation light source 2 emits the visible light or the near infrared light, the corresponding photon energy of the visible light or the near infrared light is close to the band gap energy of the semiconductor material with smaller band gap in the quantum cascade laser, electrons in the resonant cavity of the quantum cascade laser are transited to the upper energy level of conduction band laser from a valence band through photoixcitation, the number of electrons on the upper energy level of the conduction band laser is increased, the laser gain is increased, the positive amplitude modulation of the quantum cascade laser is realized, meanwhile, the number of electrons on the upper energy level of the conduction band laser is increased, the refractive index of the resonant cavity of the quantum cascade laser is changed, the effective cavity length of the resonant cavity of the quantum cascade laser is changed, the output infrared wavelength or frequency of the quantum cascade laser is changed, and the frequency modulation of the quantum cascade laser is realized; the amplitude modulation suppressing light source 3 is a visible or near infrared laser light source, and generates a laser light source with a center wavelength lambda 2 Wherein lambda is the visible or near infrared beam of 1 >λ 2 After passing through the second beam collimator 9 and the second beam focuser 10, the visible or near infrared beam is focused on the emergent end face of the quantum cascade laser 11, so that the infrared light wave output by the quantum cascade laser 1 is caused to have a frequency omega m The amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light, the amplitude modulation suppresses the visible light or the near infrared light emitted by the light source, the corresponding photon energy is far greater than the band gap energy of the semiconductor material with smaller band gap in the quantum cascade laser, the electrons in the resonant cavity of the quantum cascade laser are enabled to be transited from the valence band to the conduction band through photoexcitation, the electrons are enabled to be transited to the upper energy level of the laser through the excessively high energy, the energy level of the higher energy level and the high k state of the energy level are included, the electrons release the energy in a short time through electron-electron scattering and electron-phonon scattering mode, most of the energy increases the electron temperature in a thermal energy mode, the increase of the electron temperature increases the threshold current of the quantum cascade laser, the infrared light output power of the quantum cascade laser is further reduced, and the negative amplitude modulation is realized, meanwhile, the change of electron distribution of conduction band energy level changes the refractive 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, further changing the output infrared wavelength or frequency of the quantum cascade laser, realizing the frequency modulation of the quantum cascade laser, so when the negative amplitude modulation and the positive amplitude modulation are the same in size, the pure frequency modulation is realized, as shown in figure 3, the visible or near infrared light emitted by the frequency modulation light source 2 is shown in the left graph, the corresponding photon energy is close to the band gap energy of the semiconductor material with smaller band gap in the quantum cascade laser 1, electrons in the resonant cavity of the quantum cascade laser are transited to the energy level on the conduction band laser from the valence band through photoexcitation, further increasing the number of electrons on the energy level on the conduction band laser, increasing the laser gain, the positive amplitude modulation of the quantum cascade laser is realized, and at the same time, the increase of the number of energy level electrons on the conduction band laser changes the refractive 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 further changing the output infrared wavelength or output infrared wavelength of the quantum cascade laserThe frequency modulation of the quantum cascade laser is realized; as shown in the right graph, the amplitude modulation suppresses visible light or near infrared light emitted by the light source 3, the corresponding photon energy is far greater than the band gap energy of a semiconductor material with a smaller band gap in the quantum cascade laser 1, electrons in the resonant cavity of the quantum cascade laser are transited to a conduction band from a valence band through photoexcitation, the electrons are transited to the upper energy level of laser light by the excessively high energy, the energy level and the high-k state of the energy level are also included, in a short time, the electrons release energy in a mode of electron-electron scattering and electron-phonon scattering, most of the energy increases the electron temperature in a heat energy mode, the increase of the electron temperature increases the threshold current of the quantum cascade laser, the infrared output power of the quantum cascade laser is further reduced, the negative amplitude modulation is realized, meanwhile, the refractive index of the resonant cavity of the quantum cascade laser is changed by the change of the electron distribution of the conduction band energy level, the effective cavity length of the quantum cascade laser is further changed, the output wavelength or frequency of the quantum cascade laser is realized, and the frequency modulation of the quantum cascade laser is realized, so that when the negative amplitude modulation is as the positive amplitude and the same as the pure amplitude modulation is realized; the pure frequency modulated infrared light of the quantum cascade laser 1 passes through a beam collimator 11 and is split into two beams of light by a beam splitter 12, and one beam of light enters a Fourier transform spectrometer 13 for measuring the wavelength variation quantity; the other beam is converged on the detection surface of the high-frequency infrared detector 15 through the beam focusing device 14 and is used for measuring the amplitude variation quantity of the other beam; the high-precision oscilloscope 16 and the computer 17 are utilized to realize real-time display, analysis, processing and storage of signals.
As shown in fig. 4, when the quantum cascade laser is not modulated, the amplitude of infrared light output by the quantum cascade laser is shown as a dotted line; when only frequency modulation visible or near infrared light is focused on the emergent end face of the quantum cascade laser, the amplitude of infrared light output by the quantum cascade laser is increased, as shown by a solid line; when the amplitude modulation suppresses the focusing of visible or near infrared light on the exit end face of the quantum cascade laser, the amplitude of infrared light output by it is suppressed, as indicated by the dotted line.
As shown in fig. 5, when the quantum cascade laser is not modulated, the position of the central wavelength of the infrared light output by the quantum cascade laser is shown as a solid line; when only frequency modulation visible or near infrared light is focused on the emergent end face of the quantum cascade laser, the position of the central wavelength of infrared light output by the quantum cascade laser is blue shifted, as shown by a dotted line; when only amplitude modulation inhibits visible or near infrared light from focusing on the emergent end face of the quantum cascade laser, the position of the central wavelength of infrared light output by the quantum cascade laser shifts blue, as shown by a dotted line; when two beams of visible light or near infrared light are simultaneously focused on the emergent end face of the quantum cascade laser, the blue shift of the central wavelength position of infrared light output by the quantum cascade laser is increased, and the sum of the blue shifts caused by the two beams of light is basically the same as that caused by the two beams of light respectively, as shown by broken dotted lines.
The quantum cascade laser Quan Guangchun 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 communication.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (3)
1. All-optical pure frequency modulation system based on quantum cascade laser, characterized by including quantum cascade laser (1), high-precision current source (4), constant temperature control device (5), two light beam modulation system, beam collimator (11), beam splitter (12), fourier infrared spectrometer (13), beam focus ware (14), high-frequency infrared detector (15), high-precision oscilloscope (16), wherein:
quantum cascade laser (1): the quantum cascade laser (1) is fixed on a metal heat sink, and frequency modulation visible light or near infrared laser beams and amplitude modulation inhibition visible light or near infrared laser beams are converged on an emergent end face of the quantum cascade laser (1);
high precision current source (4): the method is used for providing direct current or a current pulse sequence with the pulse width Tp and the repetition frequency omega r for the quantum cascade laser (1) so that the quantum cascade laser (1) works in a direct current or pulse mode;
constant temperature control device (5): the method is used for providing a constant-temperature working environment for the quantum cascade laser (1) and ensuring the stable operation of the quantum cascade laser (1);
dual beam modulation system: the device is used for carrying out two kinds of modulation on light output by the quantum cascade laser (1), wherein one kind of modulation is increased, the other kind of modulation is decreased, the amplitude of the oscillation of the output light wavelength is in direct proportion to the light intensity of the visible light or the near infrared light beam, the amplitude, the frequency modulation and the amplitude suppression of the quantum cascade laser (1) are realized, the pure frequency modulation is realized, and the modulated light wave is output;
beam collimator (11): the light wave output by the quantum cascade laser (1) is collimated and regulated and output to a beam splitter (12);
beam splitter (12): dividing the light wave output by the beam collimator (11) into two beams with the same power, wherein one beam is coupled into the Fourier infrared spectrometer (13), and the other beam is focused on the detection surface of the high-frequency infrared detector (15) through the beam focusing device (14);
fourier infrared spectrometer (13): the device is used for measuring the wavelength change of the infrared light output by the quantum cascade laser (1);
high-frequency infrared detector (15): the detected optical signals are converted into electric signals and transmitted to a high-precision oscilloscope (16), and the high-precision oscilloscope (16) displays the signals.
2. An all-optical pure frequency modulation system based on quantum cascade laser according to claim 1, wherein: the dual-beam modulation system comprises a frequency modulation light source (2), an amplitude modulation suppression light source (3), a multipath synchronous output semiconductor laser driver (6), a first beam collimator (7), a first beam focusing device (8), a second beam collimator (9) and a second beam focusing device (10), wherein:
multiplex synchronous output semiconductor laser drive (6): for providing a DC or repetition frequency of amplitude aω m The current pulse sequence of (2) is used for enabling the frequency modulation light source to work in a direct current or pulse mode; at the same time providing a DC or repetition frequency of amplitude b ofω m And is synchronized with the driving current of the frequency modulated light source (2) such that the amplitude modulated suppression light source (3) operates in a direct current or pulse mode;
frequency modulated light source (2): as a visible or near infrared laser source, a laser light source with a central wavelength ofλ 1 And the visible or near-infrared light beam is focused on the emergent end face of the quantum cascade laser (1) after passing through the first light beam collimator (7) and the first light beam focusing device (8), so that the infrared light wave output by the quantum cascade laser (1) is caused to be in frequencyω m The amplitude of the oscillation is proportional to the light intensity of the visible light or the near infrared light;
amplitude modulation suppressing light source (3): as a visible or near infrared laser source, a laser light source with a central wavelength ofλ 2 In whichλ 1 >λ 2 After passing through the second beam collimator (9) and the second beam focusing device (10), the visible or near infrared beam is focused on the emergent end face of the quantum cascade laser (1), so that the infrared light wave output by the quantum cascade laser (1) is caused to have a frequencyω m The amplitude of the oscillation is proportional to the intensity of the visible or near infrared light beam.
3. An all-optical pure frequency modulation system based on quantum cascade laser according to claim 2, characterized in that: the energy of photons corresponding to visible light or near infrared light emitted by the frequency modulation light source (2) is equal to or different from the band gap energy of energy levels on the valence band top and the conduction band laser in the quantum cascade laser (1) by not more than 1 phonon energy; the amplitude modulation suppresses visible or near infrared light emitted by the light source (3) and corresponds to photon energy greater than band gap energy of energy levels on the valence band top and conduction band lasers in the quantum cascade laser (1).
Priority Applications (1)
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| CN107768977B (en) * | 2017-11-17 | 2023-06-30 | 中国工程物理研究院流体物理研究所 | Pulse regulation and control system of quantum cascade laser based on double-beam modulation |
| JP7408950B2 (en) * | 2019-08-22 | 2024-01-09 | セイコーエプソン株式会社 | Circuit devices, oscillators, real-time clock devices, electronic equipment and mobile objects |
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