Waveguide-based narrow-linewidth mid-infrared light source and control method

Abstract

The application provides a waveguide-based narrow linewidth mid-infrared light source and a control method. A first laser source is used to output first continuous infrared laser; a second laser source is used to output second continuous infrared laser; a laser frequency locking module is used to perform feedback control on the first laser source to lock the frequency of the first continuous infrared laser; a laser frequency control module is used to perform feedback control on the second laser source to stabilize and tune the frequency of the second continuous infrared laser; a laser and waveguide coupling module is used to couple the first continuous infrared laser and the second continuous infrared laser into a waveguide module; a temperature control module is used to control the temperature of the waveguide module to make the difference frequency process meet the phase matching condition; and the waveguide module is used to make the first continuous infrared laser and the second continuous infrared laser generate difference frequency to obtain mid-infrared laser. Thus, the purposes of high-power output, narrow linewidth output, wide-range tuning and long-term frequency stability of mid-infrared laser are achieved in a compact system.

Description

Technical Field

[0001] This invention relates to the field of laser technology, specifically to a waveguide-based narrow-linewidth mid-infrared light source and its control method. Background Technology

[0002] Single-mode mid-infrared laser sources are the cornerstone of precision molecular spectroscopy, widely used in cutting-edge fields such as two-photon and multi-photon mid-infrared spectroscopy, molecular selective quantum manipulation, and saturable absorption measurement. These applications place multi-dimensional performance requirements on the light source: high output power to excite weak transitions, kilohertz-level narrow linewidths to resolve narrow spectral features and maintain quantum coherence, broad non-mode-hopping tuning capability to achieve wide-range spectral scanning, and metrological-grade long-term frequency stability. The mid-infrared band encompasses a large number of molecular fundamental vibrational transitions, with intensities one to two orders of magnitude higher than the near-infrared or visible overtone bands, significantly improving detection sensitivity. Combined with techniques such as ultrasonic expansion or cold molecule preparation, mid-infrared laser sources provide a powerful platform for transient species detection and quantum-state resolved measurements.

[0003] However, existing MIR laser technologies struggle to simultaneously meet these performance indicators in a single compact system, resulting in persistent technical bottlenecks. Current mainstream solutions and their limitations are as follows: gas lasers, while exhibiting narrow linewidths and excellent frequency stability, suffer from extremely limited tuning capabilities due to the constraints of discrete molecular transitions in their output wavelength; quantum cascade lasers, despite their small size, high power, and wide wavelength coverage, have free-running linewidths in the megahertz range, making narrow linewidth output difficult; traditional crystal-based difference-frequency sources, while offering wide tuning ranges and narrow instantaneous linewidths, suffer from weak optical field confinement, short interaction lengths, low optical-to-optical conversion efficiency, and output power typically below milliwatts; continuous-wave optical parametric oscillators (CSOs) are considered the platform with the greatest potential for balancing multiple performance indicators, but achieving a harmonious balance between high power and wide tuning remains challenging, and their poor stability also limits their applications.

[0004] In summary, gas lasers suffer from limited tuning, quantum cascade lasers lack sufficient linewidth, traditional difference-frequency light sources have insufficient power, and continuous-wave parametric oscillators exhibit poor parameter balance and stability. Therefore, there is an urgent need in this field for a novel mid-infrared light source solution that integrates high power, narrow linewidth, wide tuning range, and long-term frequency stability within a compact system. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a waveguide-based narrow-linewidth mid-infrared light source and control method to achieve high-power output, narrow-linewidth output, wide-range tuning, and long-term frequency stability of mid-infrared lasers in a compact system.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] The first aspect of this invention discloses a narrow linewidth mid-infrared light source based on a waveguide, comprising: a first laser source, a second laser source, a laser frequency locking module, a laser frequency control module, a laser-waveguide coupling module, a waveguide module, and a temperature control module;

[0008] The first laser source is used to output the first continuous infrared laser;

[0009] The second laser source is used to output a second continuous infrared laser.

[0010] The laser frequency locking module includes a first infrared frequency reference for providing a first stable characteristic frequency signal; the laser frequency locking module is used to perform feedback control on the first laser source based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser.

[0011] The laser frequency control module includes a second infrared frequency reference for providing a second stable characteristic frequency signal; the laser frequency control module is used to perform feedback control on the second laser source based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser.

[0012] The laser-waveguide coupling module is used to couple the first continuous infrared laser and the second continuous infrared laser to the waveguide module.

[0013] The temperature control module is used to control the temperature of the waveguide module so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module satisfies the phase matching condition.

[0014] The waveguide module is used to cause the first continuous infrared laser and the second continuous infrared laser to have a frequency difference under the phase matching condition, so as to obtain a mid-infrared laser.

[0015] Optionally, the laser frequency locking module includes: a first infrared frequency reference, a first modulation and demodulation unit, and a first negative feedback unit;

[0016] The first modulation and demodulation unit is used to modulate and demodulate the frequency and phase of the first continuous infrared laser based on the first stable characteristic frequency signal provided by the first infrared frequency reference, so as to obtain a first error signal;

[0017] The first negative feedback unit is used to perform feedback control on the first laser source according to the first error signal, so as to lock the frequency of the first continuous infrared laser at the frequency corresponding to the first stable characteristic frequency signal.

[0018] Optionally, the laser frequency control module includes: a second infrared frequency reference, an electro-optic crystal, a second modulation and demodulation unit, a second negative feedback unit, and a radio frequency source;

[0019] The electro-optic crystal is used to modulate the second continuous infrared laser according to the radio frequency signal provided by the radio frequency source to generate a laser sideband; the frequency difference between the laser sideband and the second continuous infrared laser is determined by the frequency of the radio frequency signal.

[0020] The second modulation and demodulation unit is used to modulate and demodulate the laser sideband based on the second stable characteristic frequency signal provided by the second infrared frequency reference to obtain the second error signal;

[0021] The second negative feedback unit is used to perform feedback control on the second laser source according to the second error signal, so as to lock the frequency of the laser sideband at the frequency corresponding to the second stable characteristic frequency signal;

[0022] The radio frequency source is used to adjust the frequency of the radio frequency signal to tune the frequency of the second continuous infrared laser.

[0023] Optionally, the laser-waveguide coupling module includes: an optical fiber isolator, a polarization control unit, a wavelength division multiplexing unit, and a waveguide input unit;

[0024] The fiber optic isolator is disposed in the transmission optical path of the first continuous infrared laser and the second continuous infrared laser to suppress backlight propagating in the direction toward the first laser source and the second laser source;

[0025] The polarization control unit is disposed between the fiber optic isolator and the wavelength division multiplexing unit, and is used to adjust the polarization state of the first continuous infrared laser and the second continuous infrared laser so that the polarization directions of the first continuous infrared laser and the second continuous infrared laser are the same.

[0026] The wavelength division multiplexing unit is used to combine the polarization-adjusted first continuous infrared laser and the second continuous infrared laser into the same optical fiber;

[0027] The waveguide input unit is disposed between the wavelength division multiplexing unit and the waveguide module, and is used to couple the combined first continuous infrared laser and the second continuous infrared laser to the waveguide module.

[0028] Optionally, the fiber optic isolator provides greater than 30 dB isolation for the reverse light;

[0029] Both the first and second continuous infrared lasers, after being adjusted by the polarization control unit, are linearly polarized light, and their polarization suppression ratios are both greater than 15dB.

[0030] After combining the first continuous infrared laser and the second continuous infrared laser, the wavelength division multiplexing unit maintains that the polarization directions of the first continuous infrared laser and the second continuous infrared laser are the same, and the polarization suppression ratio is greater than 15dB for both.

[0031] The waveguide input unit couples the combined first and second continuous infrared laser beams into the waveguide module with a coupling efficiency greater than 50%.

[0032] Optionally, the waveguide module includes: a magnesium oxide-doped periodically polarized lithium niobate thin-film ridge waveguide.

[0033] Optionally, the temperature control module includes: an on-chip integrated semiconductor cooling chip and a third negative feedback unit;

[0034] The on-chip integrated semiconductor cooling chip is thermally coupled to the waveguide module and is used to adjust the temperature of the waveguide module according to the temperature control signal.

[0035] The third negative feedback unit is used to detect the temperature of the waveguide module, generate the temperature control signal based on the deviation between the detected temperature and the target temperature, and control the on-chip integrated semiconductor cooling chip based on the temperature control signal to stabilize the temperature of the waveguide module at the target temperature; wherein, the target temperature is the temperature at which the difference frequency process satisfies the phase matching condition.

[0036] Optionally, the heat dissipation power of the on-chip integrated semiconductor cooling chip is not less than 1W.

[0037] Optionally, the output linewidth of both the first laser source and the second laser source is less than 1MHz;

[0038] The output power of both the first laser source and the second laser source is greater than 500mW.

[0039] A second aspect of this invention discloses a control method for a narrow-linewidth mid-infrared light source based on a waveguide, comprising:

[0040] Control the first laser source to output a first continuous infrared laser, and control the second laser source to output a second continuous infrared laser;

[0041] A first stable characteristic frequency signal is provided by a first infrared frequency reference, and the first laser source is subjected to feedback control based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser.

[0042] A second stable characteristic frequency signal is provided by a second infrared frequency reference, and the second laser source is subjected to feedback control based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser.

[0043] The first continuous infrared laser and the second continuous infrared laser are coupled and input to the waveguide module;

[0044] The temperature of the waveguide module is controlled so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module satisfies the phase matching condition.

[0045] Under the phase-matching condition, the first continuous infrared laser and the second continuous infrared laser are made to have a difference frequency in the waveguide module to obtain a mid-infrared laser.

[0046] A narrow-linewidth mid-infrared light source and control method based on waveguides, provided by the above embodiments of the present invention, includes: a first laser source, a second laser source, a laser frequency locking module, a laser frequency control module, a laser-waveguide coupling module, a waveguide module, and a temperature control module; the first laser source is used to output a first continuous infrared laser; the second laser source is used to output a second continuous infrared laser; the laser frequency locking module includes a first infrared frequency reference for providing a first stable characteristic frequency signal; the laser frequency locking module is used to perform feedback control on the first laser source based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser; the laser frequency control module includes a first infrared frequency reference for providing a second stable characteristic frequency signal. The system includes a second infrared frequency reference for the characteristic frequency signal; a laser frequency control module for feedback control of the second laser source based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser; a laser-waveguide coupling module for coupling the first and second continuous infrared lasers to the waveguide module; a temperature control module for controlling the temperature of the waveguide module to ensure that the difference frequency process of the first and second continuous infrared lasers in the waveguide module satisfies the phase matching condition; and a waveguide module for causing the first and second continuous infrared lasers to have a difference frequency under the phase matching condition to obtain a mid-infrared laser. In this scheme, by locking the frequency of the first continuous infrared laser and stabilizing and tuning the frequency of the second continuous infrared laser, the two continuous infrared lasers are efficiently coupled to the waveguide, and the phase matching condition of the difference frequency process is satisfied by waveguide temperature control. This achieves high-power output, narrow-linewidth output, wide-range tuning, and long-term frequency stability of the mid-infrared laser within a compact system. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0048] Figure 1 This is a structural diagram of a waveguide-based narrow-linewidth mid-infrared light source disclosed in an embodiment of the present invention;

[0049] Figure 2 This is a flowchart of a control method for a narrow linewidth mid-infrared light source based on a waveguide, as disclosed in an embodiment of the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0052] As the background technology shows, in existing technologies, gas lasers have limited tuning capabilities, quantum cascade lasers have insufficient linewidth, traditional difference-frequency light sources have insufficient power, and continuous-wave parametric oscillators suffer from poor parameter balance and stability. There is an urgent need in this field for a novel mid-infrared light source solution that integrates high power, narrow linewidth, wide tuning range, and long-term frequency stability within a compact system.

[0053] Therefore, this invention provides a waveguide-based narrow-linewidth mid-infrared light source and its control method. In this scheme, by locking the frequency of a first continuous infrared laser and stabilizing and tuning the frequency of a second continuous infrared laser, the two continuous infrared laser beams are efficiently coupled to a waveguide. Waveguide temperature control is used to satisfy the phase-matching condition of the difference frequency process, thereby achieving high-power output, narrow-linewidth output, wide-range tuning, and long-term frequency stability of the mid-infrared laser within a compact system. Specifically, it can achieve 10nm mode-free continuous tuning, 10mW-level power output, kilohertz-level narrow linewidth, 4-5µm wavelength coverage, and metrological-grade long-term frequency stability within a compact system. Spectral detection based on this mid-infrared light source has wide application value in atmospheric environmental monitoring, laser spectroscopy research, and molecular quantum state modulation.

[0054] First, it should be noted that the basic principle of this invention is to generate mid-infrared laser by using two lasers in a waveguide with a frequency difference. The frequency of one laser beam is stabilized by locking its frequency to a frequency reference. The frequency of the other laser beam is tuned by precisely controlling its frequency, thereby tuning the frequency of the mid-infrared laser. Since the conversion efficiency of the difference-frequency nonlinear effect is proportional to the product of the powers of the two laser beams, controlling the coupling between the laser and the waveguide, and precisely controlling the waveguide temperature to control phase matching, can greatly improve the nonlinear conversion efficiency and achieve high-power output of the mid-infrared laser. Because the linewidth of the mid-infrared laser is equal to the sum of the linewidths of the two laser beams with different frequencies, the linewidth of the mid-infrared laser is narrowed by locking the frequency of one laser beam and precisely controlling the frequency and linewidth of the other laser beam. This is illustrated in the following embodiments:

[0055] like Figure 1 The diagram shown is a structural diagram of a narrow linewidth mid-infrared light source based on a waveguide disclosed in an embodiment of the present invention, including a first laser source 1, a second laser source 2, a laser frequency locking module 3, a laser frequency control module 4, a laser-waveguide coupling module 5, a waveguide module 6, and a temperature control module 7.

[0056] In this system, the first laser source 1 is used to output a first continuous infrared laser, and the second laser source 2 is used to output a second continuous infrared laser. The first and second continuous infrared lasers serve as two pump lasers for the difference frequency process.

[0057] The first and second continuous infrared lasers are continuous infrared lasers with specially selected wavelengths, and their output wavelengths can be quickly tuned.

[0058] In one optional embodiment, both the first laser source 1 and the second laser source 2 are frequency-tunable continuous infrared laser sources. The output linewidth of both the first laser source 1 and the second laser source 2 is less than 1 MHz, and the output power of both is greater than 500 mW.

[0059] It should be noted that the output frequencies of the first laser source 1 and the second laser source 2 are selected based on the frequency of the mid-infrared laser to be generated and the phase matching range of the waveguide module 6. The first continuous infrared laser and the second continuous infrared laser have different frequencies, and the frequency difference between them corresponds to the frequency of the mid-infrared laser to be generated.

[0060] The laser frequency locking module 3 is used to perform feedback control on the first laser source based on the first stable characteristic frequency signal in order to lock the frequency of the first continuous infrared laser.

[0061] The laser frequency locking module 3 includes a first infrared frequency reference, a first modulation and demodulation unit, and a first negative feedback unit.

[0062] The first infrared frequency reference is used to provide a first stable characteristic frequency signal. The first stable characteristic frequency signal serves as the frequency locking reference for the first continuous infrared laser. The first infrared frequency reference can be a frequency reference device capable of providing a stable optical characteristic frequency, and its specific structure is not limited.

[0063] The first modulation and demodulation unit is used to modulate and demodulate the frequency and phase of the first continuous infrared laser based on the first stable characteristic frequency signal to obtain the first error signal.

[0064] Specifically, the first modulation and demodulation unit applies frequency modulation and / or phase modulation to the first continuous infrared laser, and demodulates the signal characterizing the frequency deviation of the first continuous infrared laser frequency relative to the first stable characteristic frequency signal. The polarity of the first error signal is used to characterize the direction of the frequency offset of the first continuous infrared laser relative to the locked frequency, and the amplitude of the first error signal is used to characterize the corresponding frequency offset.

[0065] The first negative feedback unit is connected to the first modulation and demodulation unit and the first laser source 1, and is used to perform feedback control on the first laser source according to the first error signal, so as to lock the frequency of the first continuous infrared laser at the frequency corresponding to the first stable characteristic frequency signal.

[0066] Specifically, the first negative feedback unit generates a first feedback control signal based on the first error signal and applies the first feedback control signal to the frequency adjustment terminal of the first laser source 1.

[0067] When the frequency of the first continuous infrared laser deviates from the frequency corresponding to the first stable characteristic frequency signal, the first modulation and demodulation unit generates a corresponding first error signal. The first negative feedback unit adjusts the first laser source 1 according to the first error signal to reduce the first error signal and locks the frequency of the first continuous infrared laser at the frequency corresponding to the first stable characteristic frequency signal.

[0068] Therefore, the frequency drift of the first laser source 1 caused by factors such as ambient temperature, mechanical vibration, and changes in driving parameters can be suppressed, thereby improving the frequency stability of the first continuous infrared laser.

[0069] The laser frequency control module 4 is used to perform feedback control on the second laser source based on the second stable characteristic frequency signal, so as to stabilize and tune the frequency of the second continuous infrared laser.

[0070] The laser frequency control module 4 includes a second infrared frequency reference, an electro-optic crystal, a second modulation and demodulation unit, a second negative feedback unit, and a radio frequency source.

[0071] The second infrared frequency reference is used to provide a second stable characteristic frequency signal, which serves as a frequency locking reference for the laser sideband.

[0072] The radio frequency (RF) frequency source is used to provide a frequency-tunable RF signal to the electro-optic crystal. The electro-optic crystal is placed in the transmission optical path of the second continuous infrared laser and is used to electro-optically modulate the second continuous infrared laser according to the RF signal to generate laser sidebands.

[0073] The frequency difference between the laser sideband and the carrier frequency of the second continuous infrared laser is determined by the frequency of the radio frequency signal. Changing the frequency of the radio frequency signal changes the frequency interval between the laser sideband and the second continuous infrared laser.

[0074] The second modulation and demodulation unit modulates and demodulates the laser sideband based on the second stable characteristic frequency signal provided by the second infrared frequency reference, to obtain the second error signal. The second error signal characterizes the deviation of the laser sideband frequency from the corresponding frequency of the second stable characteristic frequency signal.

[0075] The second negative feedback unit is used to perform feedback control on the second laser source based on the second error signal, so as to lock the frequency of the laser sideband at the frequency corresponding to the second stable characteristic frequency signal.

[0076] Specifically, the second negative feedback unit generates a second feedback control signal based on the second error signal, and uses the second feedback control signal to adjust the second laser source 2 so that the frequency of the laser sideband generated by the electro-optic crystal is locked at the frequency corresponding to the second stable characteristic frequency signal.

[0077] The feedback bandwidth of the first and second negative feedback units can be set according to the output linewidth of the corresponding laser source. When the output linewidth of the laser source is narrow, a relatively small feedback bandwidth can be used.

[0078] Radio frequency source, used to adjust the frequency of radio frequency signal to tune the frequency of the second continuous infrared laser.

[0079] In this embodiment, the radio frequency source adjusts the frequency of the radio frequency signal within a preset radio frequency range, enabling the second laser source 2 to achieve a frequency tuning bandwidth of 1 MHz under the control of the laser frequency control module 4. The frequency tuning bandwidth refers to the frequency range within which the center frequency of the second continuous infrared laser can be adjusted under the control of the laser frequency control module 4. The 1 MHz frequency tuning bandwidth is a tuning range selected in this embodiment based on specific application requirements and does not constitute a limitation on the maximum frequency tuning range that the second laser source 2 itself can achieve.

[0080] It should be noted that, in the closed-loop locked state, when the RF frequency source adjusts the frequency of the RF signal, the frequency interval between the laser sideband and the second continuous infrared laser changes. The second negative feedback unit adjusts the output frequency of the second laser source 2 according to the corresponding second error signal, so that the laser sideband continues to be maintained at the frequency corresponding to the second stable characteristic frequency signal, thereby causing the frequency of the second continuous infrared laser to change accordingly.

[0081] Therefore, the laser frequency control module 4 can use the second infrared frequency reference as a stable benchmark to achieve precise tuning of the second continuous infrared laser frequency by adjusting the radio frequency signal frequency, while maintaining the frequency stability of the second continuous infrared laser.

[0082] Since the frequency of the first continuous infrared laser is locked, the frequency of the second continuous infrared laser can be stabilized and tuned. Therefore, adjusting the frequency of the second continuous infrared laser can change the frequency difference between the first and second continuous infrared lasers, thereby tuning the frequency of the mid-infrared laser generated by the difference frequency.

[0083] The laser-waveguide coupling module 5 is located between the first laser source 1, the second laser source 2 and the waveguide module 6, and is used to couple the first continuous infrared laser and the second continuous infrared laser into the waveguide module 6.

[0084] The laser-waveguide coupling module 5 includes an optical fiber isolator, a polarization control unit, a wavelength division multiplexing unit, and a waveguide input unit.

[0085] An optical fiber isolator is disposed in the transmission optical path of the first continuous infrared laser and the second continuous infrared laser to allow the first continuous infrared laser and the second continuous infrared laser to transmit in the direction toward the waveguide module 6, and to suppress the reverse light propagating in the direction toward the first laser source 1 and the second laser source 2.

[0086] The backlight can be light reflected or scattered by the wavelength division multiplexing unit, waveguide input unit, input end face of waveguide module 6, or other subsequent optical devices. By suppressing the backlight from entering the first laser source 1 and the second laser source 2, the impact of optical feedback on the laser output frequency, output power, and operational stability can be reduced.

[0087] In practice, fiber optic isolators can be installed in the transmission optical paths of the first and second continuous infrared lasers, respectively. The isolation of the fiber optic isolators from reverse light is greater than 30 dB.

[0088] The polarization control unit is located between the fiber optic isolator and the wavelength division multiplexing unit. It is used to adjust the polarization state of the first continuous infrared laser and the second continuous infrared laser respectively, so that both the first continuous infrared laser and the second continuous infrared laser become linearly polarized light and have the same polarization direction.

[0089] The polarization suppression ratios of both the first and second continuous infrared lasers, after adjustment by the polarization control unit, are greater than 15 dB. By matching the polarization directions of the two continuous infrared lasers with the target polarization mode supported by the waveguide module 6, the coupling efficiency between the two continuous infrared lasers and the waveguide module 6 can be improved, as well as the difference frequency conversion efficiency.

[0090] The wavelength division multiplexing (WDM) unit is used to combine a first continuous infrared laser and a second continuous infrared laser, both polarization-adjusted and of different frequencies, into the same optical fiber. After combining the laser beams, the WDM unit maintains the same polarization direction for both the first and second continuous infrared lasers and ensures that their polarization suppression ratios are both greater than 15 dB.

[0091] The waveguide input unit is located between the wavelength division multiplexing unit and the waveguide module 6, and is used to couple the first continuous infrared laser and the second continuous infrared laser after beam combining to the waveguide module 6.

[0092] The waveguide input unit can adjust the beam size and perform mode matching on the two combined continuous infrared laser beams, coupling them into the target transmission mode of the waveguide module 6. In this embodiment, the coupling efficiency of the waveguide input unit in coupling the first and second combined continuous infrared laser beams into the waveguide module 6 is greater than 50%.

[0093] Among them, waveguide module 6 includes a periodically polarized lithium niobate thin film ridge waveguide doped with magnesium oxide (MgO).

[0094] In one specific embodiment, the thin-film ridge waveguide is a periodically polarized lithium niobate waveguide chip with a length of 10 mm. Magnesium oxide doping is beneficial to improving the resistance of the lithium niobate waveguide to optical damage. The thin-film ridge structure can laterally confine the first and second continuous infrared lasers, increase the optical power density inside the waveguide, and extend the effective nonlinear action length of the two continuous infrared laser beams.

[0095] The periodic polarization structure is used to compensate for the phase mismatch between the first continuous infrared laser, the second continuous infrared laser and the mid-infrared laser during the difference frequency process, so that the difference frequency process satisfies the quasi-phase matching condition.

[0096] After the first and second continuous infrared lasers are coupled into the same thin-film ridge waveguide, they propagate together in the waveguide and undergo a second-order nonlinear difference frequency process to generate mid-infrared laser.

[0097] If the frequency of the first continuous infrared laser is f1 and the frequency of the second continuous infrared laser is f2, then the frequency of the generated mid-infrared laser is f1. MIR Satisfy: f MIR =|f1-f2|.

[0098] By locking the frequency of the first continuous infrared laser and stabilizing and tuning the frequency of the second continuous infrared laser, the output frequency and linewidth of the mid-infrared laser can be controlled.

[0099] Compared to difference frequency devices using bulk nonlinear crystals, thin-film ridge waveguides can improve the optical field confinement capability and nonlinear interaction strength, thereby improving the conversion efficiency of the first and second continuous infrared lasers to mid-infrared lasers.

[0100] The temperature control module 7 is used to control the temperature of the waveguide module 6 so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module 6 satisfies the phase matching condition.

[0101] The temperature control module 7 includes an on-chip integrated thermoelectric cooler and a third negative feedback unit. The on-chip integrated thermoelectric cooler is thermally coupled to the waveguide module 6. Specifically, the on-chip integrated thermoelectric cooler can be closely attached to the waveguide chip of the waveguide module 6 to improve the heat conduction efficiency between the two.

[0102] An on-chip integrated thermoelectric cooler is used to adjust the temperature of waveguide module 6 according to a temperature control signal. In this embodiment, the heat dissipation power of the on-chip integrated thermoelectric cooler is not less than 1W.

[0103] The third negative feedback unit is used to detect the temperature of the waveguide module 6, generate a temperature control signal based on the deviation between the detected temperature and the target temperature, and control the on-chip integrated semiconductor cooling chip based on the temperature control signal to stabilize the temperature of the waveguide module 6 at the target temperature.

[0104] The third negative feedback unit may include a temperature sensing element, a temperature comparison circuit, and a driving circuit. The temperature sensing element is located near or thermally coupled to the waveguide module 6 to obtain the actual temperature of the waveguide module 6; the temperature comparison circuit is used to determine the deviation between the actual temperature and the target temperature; and the driving circuit adjusts the operating state of the on-chip integrated semiconductor cooling chip according to the deviation.

[0105] The target temperature is the temperature at which the difference frequency process of the first and second continuous infrared lasers in waveguide module 6 satisfies the phase matching condition. The temperature of waveguide module 6 can be pre-changed, and the output power of the mid-infrared laser can be detected. The waveguide temperature corresponding to when the mid-infrared laser output power meets the preset requirement is determined as the target temperature.

[0106] In one specific embodiment, the third negative feedback unit enables the waveguide module 6 to achieve a temperature stability of 0.005℃. By precisely controlling the temperature of the waveguide module 6, changes in waveguide refractive index and phase mismatch caused by ambient temperature variations can be suppressed, maintaining the phase matching state of the difference frequency process.

[0107] Based on the aforementioned structure of the waveguide-based narrow-linewidth mid-infrared light source, the generation process of mid-infrared laser is as follows:

[0108] First laser source 1 and second laser source 2 output first continuous infrared laser and second continuous infrared laser, respectively. Laser frequency locking module 3 locks the frequency of the first continuous infrared laser to the frequency corresponding to the first stable characteristic frequency signal. Laser frequency control module 4 locks the laser sideband generated by the second continuous infrared laser to the frequency corresponding to the second stable characteristic frequency signal, and tunes the frequency of the second continuous infrared laser by changing the radio frequency signal frequency. After fiber isolation and polarization adjustment, the first and second continuous infrared lasers are combined into the same fiber by a wavelength division multiplexing unit, and then coupled into waveguide module 6 by a waveguide input unit. Temperature control module 7 controls the temperature of waveguide module 6 to ensure that the difference frequency process of the two continuous infrared lasers in waveguide module 6 meets the phase matching condition. The difference frequency of the two continuous infrared lasers in waveguide module 6 produces mid-infrared laser. Because the frequency of the first continuous infrared laser is locked, the frequency of the second continuous infrared laser is stabilized and can be precisely tuned, thus reducing the impact of frequency drift of the two pump lasers on the frequency and linewidth of the mid-infrared laser. Meanwhile, the laser-waveguide coupling module 5 improves the coupling efficiency of two continuous infrared laser beams entering the waveguide module 6, the thin-film ridge waveguide increases the optical power density within the waveguide, and the temperature control module 7 maintains the phase matching state of the difference frequency process, thereby improving the conversion efficiency and output stability of the mid-infrared laser.

[0109] In summary, the waveguide-based narrow-linewidth mid-infrared light source disclosed in this invention achieves the goals of high-power output, narrow-linewidth output, wide-range tuning, and long-term frequency stability of mid-infrared laser within a compact system.

[0110] like Figure 2 The diagram shown is a flowchart of a control method for a waveguide-based narrow-linewidth mid-infrared light source disclosed in an embodiment of the present invention. This control method can be applied to any of the waveguide-based narrow-linewidth mid-infrared light sources disclosed in the above embodiments, and includes the following steps.

[0111] Step S101: Control the first laser source to output the first continuous infrared laser, and control the second laser source to output the second continuous infrared laser.

[0112] The frequencies of the first and second continuous infrared lasers are determined based on the frequency of the mid-infrared laser to be generated and the phase matching range of the waveguide module. The first and second continuous infrared lasers have different frequencies and serve as pump lasers for the difference frequency process.

[0113] Step S102: Provide a first stable characteristic frequency signal through a first infrared frequency reference, and perform feedback control on the first laser source based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser.

[0114] Specifically, the frequency and phase of the first continuous infrared laser are modulated and demodulated to obtain a first error signal; a first feedback control signal is generated based on the first error signal; and the first laser source is adjusted using the first feedback control signal so that the frequency of the first continuous infrared laser is locked at the frequency corresponding to the first stable characteristic frequency signal.

[0115] Step S103: Provide a second stable characteristic frequency signal through a second infrared frequency reference, and perform feedback control on the second laser source based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser.

[0116] Specifically, an RF signal is provided to the electro-optic crystal using an RF frequency source; the electro-optic crystal modulates the second continuous infrared laser according to the RF signal to generate a laser sideband; the laser sideband is modulated and demodulated to obtain a second error signal; the second laser source is fed back and controlled according to the second error signal to lock the frequency of the laser sideband at the frequency corresponding to the second stable characteristic frequency signal.

[0117] When the frequency of the radio frequency signal is adjusted, the second negative feedback unit adjusts the output frequency of the second laser source accordingly, so that the laser sideband is frequency locked, thereby tuning the frequency of the second continuous infrared laser.

[0118] Step S104: Couple the first continuous infrared laser and the second continuous infrared laser to the waveguide module.

[0119] Specifically, the reverse light propagating in the direction of the first laser source and the second laser source is isolated; the polarization state of the first continuous infrared laser and the second continuous infrared laser is adjusted so that both are linearly polarized light and have the same polarization direction; the two continuous infrared laser beams are combined into the same optical fiber; and the two combined continuous infrared laser beams are coupled into the waveguide module.

[0120] Step S105: Control the temperature of the waveguide module so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module satisfies the phase matching condition.

[0121] Specifically, the actual temperature of the waveguide module is detected; the deviation between the actual temperature and the target temperature is determined; a temperature control signal is generated based on the deviation; and the on-chip integrated semiconductor cooling chip is controlled based on the temperature control signal to stabilize the temperature of the waveguide module at the target temperature.

[0122] Step S106: Under phase-matching conditions, the first continuous infrared laser and the second continuous infrared laser are made to have a difference frequency in the waveguide module to obtain a mid-infrared laser.

[0123] By adjusting the frequency of the second continuous infrared laser, the frequency difference between the first and second continuous infrared lasers can be adjusted, thereby adjusting the frequency of the mid-infrared laser.

[0124] It should be noted that the numbering of steps S101 to S106 is mainly used to distinguish different processing procedures and does not constitute an absolute limitation on the order of execution of each step. For example, frequency locking of the first continuous infrared laser, frequency control of the second continuous infrared laser, and temperature control of the waveguide module can be performed simultaneously or continuously.

[0125] Based on the waveguide-based narrow-linewidth mid-infrared light source and control method provided in the above embodiments, by locking the frequency of the first continuous infrared laser and stabilizing and tuning the frequency of the second continuous infrared laser, the two continuous infrared lasers are coupled to the waveguide with high efficiency. The phase matching condition of the difference frequency process is satisfied by using waveguide temperature control, thereby achieving the purpose of high-power output, narrow-linewidth output, wide-range tuning and long-term frequency stability of mid-infrared laser in a compact system.

[0126] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0127] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0128] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A waveguide-based narrow-linewidth mid-infrared light source, characterized in that, include: The system comprises a first laser source, a second laser source, a laser frequency locking module, a laser frequency control module, a laser-waveguide coupling module, a waveguide module, and a temperature control module. The first laser source is used to output the first continuous infrared laser; The second laser source is used to output a second continuous infrared laser. The laser frequency locking module includes a first infrared frequency reference for providing a first stable characteristic frequency signal; the laser frequency locking module is used to perform feedback control on the first laser source based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser. The laser frequency control module includes a second infrared frequency reference for providing a second stable characteristic frequency signal; the laser frequency control module is used to perform feedback control on the second laser source based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser. The laser-waveguide coupling module is used to couple the first continuous infrared laser and the second continuous infrared laser to the waveguide module. The temperature control module is used to control the temperature of the waveguide module so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module satisfies the phase matching condition. The waveguide module is used to cause the first continuous infrared laser and the second continuous infrared laser to have a frequency difference under the phase matching condition, so as to obtain a mid-infrared laser.

2. The waveguide-based narrow-linewidth mid-infrared light source according to claim 1, characterized in that, The laser frequency locking module includes: a first infrared frequency reference, a first modulation and demodulation unit, and a first negative feedback unit; The first modulation and demodulation unit is used to modulate and demodulate the frequency and phase of the first continuous infrared laser based on the first stable characteristic frequency signal provided by the first infrared frequency reference, so as to obtain a first error signal; The first negative feedback unit is used to perform feedback control on the first laser source according to the first error signal, so as to lock the frequency of the first continuous infrared laser at the frequency corresponding to the first stable characteristic frequency signal.

3. The waveguide-based narrow-linewidth mid-infrared light source according to claim 1, characterized in that, The laser frequency control module includes: a second infrared frequency reference, an electro-optic crystal, a second modulation and demodulation unit, a second negative feedback unit, and a radio frequency source; The electro-optic crystal is used to modulate the second continuous infrared laser according to the radio frequency signal provided by the radio frequency source to generate a laser sideband; the frequency difference between the laser sideband and the second continuous infrared laser is determined by the frequency of the radio frequency signal. The second modulation and demodulation unit is used to modulate and demodulate the laser sideband based on the second stable characteristic frequency signal provided by the second infrared frequency reference to obtain the second error signal; The second negative feedback unit is used to perform feedback control on the second laser source according to the second error signal, so as to lock the frequency of the laser sideband at the frequency corresponding to the second stable characteristic frequency signal; The radio frequency source is used to adjust the frequency of the radio frequency signal to tune the frequency of the second continuous infrared laser.

4. The waveguide-based narrow-linewidth mid-infrared light source according to claim 1, characterized in that, The laser-waveguide coupling module includes: an optical fiber isolator, a polarization control unit, a wavelength division multiplexing unit, and a waveguide input unit; The fiber optic isolator is disposed in the transmission optical path of the first continuous infrared laser and the second continuous infrared laser, and is used to suppress backlight propagating in the direction toward the first laser source and the second laser source; The polarization control unit is disposed between the fiber optic isolator and the wavelength division multiplexing unit, and is used to adjust the polarization state of the first continuous infrared laser and the second continuous infrared laser so that the polarization directions of the first continuous infrared laser and the second continuous infrared laser are the same. The wavelength division multiplexing unit is used to combine the polarization-adjusted first continuous infrared laser and the second continuous infrared laser into the same optical fiber; The waveguide input unit is disposed between the wavelength division multiplexing unit and the waveguide module, and is used to couple the first continuous infrared laser and the second continuous infrared laser after beam combining to the waveguide module.

5. The waveguide-based narrow-linewidth mid-infrared light source according to claim 4, characterized in that, The fiber optic isolator provides greater than 30 dB isolation for the reverse light. Both the first and second continuous infrared lasers, after being adjusted by the polarization control unit, are linearly polarized light, and their polarization suppression ratios are both greater than 15dB. After combining the first continuous infrared laser and the second continuous infrared laser, the wavelength division multiplexing unit maintains that the polarization directions of the first continuous infrared laser and the second continuous infrared laser are the same, and the polarization suppression ratio of both is greater than 15dB. The waveguide input unit couples the combined first and second continuous infrared laser beams into the waveguide module with a coupling efficiency greater than 50%.

6. The waveguide-based narrow-linewidth mid-infrared light source according to claim 1, characterized in that, The waveguide module includes: a magnesium oxide-doped periodically polarized lithium niobate thin film ridge waveguide.

7. The waveguide-based narrow-linewidth mid-infrared light source according to claim 1, characterized in that, The temperature control module includes: an on-chip integrated semiconductor cooling chip and a third negative feedback unit; The on-chip integrated semiconductor cooling chip is thermally coupled to the waveguide module and is used to adjust the temperature of the waveguide module according to the temperature control signal. The third negative feedback unit is used to detect the temperature of the waveguide module, generate the temperature control signal based on the deviation between the detected temperature and the target temperature, and control the on-chip integrated semiconductor cooling chip based on the temperature control signal to stabilize the temperature of the waveguide module at the target temperature; wherein, the target temperature is the temperature at which the difference frequency process satisfies the phase matching condition.

8. The waveguide-based narrow-linewidth mid-infrared light source according to claim 7, characterized in that, The heat dissipation power of the on-chip integrated semiconductor cooling chip is not less than 1W.

9. The waveguide-based narrow-linewidth mid-infrared light source according to any one of claims 1 to 8, characterized in that, The output linewidth of both the first laser source and the second laser source is less than 1MHz; The output power of both the first laser source and the second laser source is greater than 500mW.

10. A control method for a narrow-linewidth mid-infrared light source based on waveguides, characterized in that, include: Control the first laser source to output a first continuous infrared laser, and control the second laser source to output a second continuous infrared laser; A first stable characteristic frequency signal is provided by a first infrared frequency reference, and the first laser source is subjected to feedback control based on the first stable characteristic frequency signal to lock the frequency of the first continuous infrared laser. A second stable characteristic frequency signal is provided by a second infrared frequency reference, and the second laser source is subjected to feedback control based on the second stable characteristic frequency signal to stabilize and tune the frequency of the second continuous infrared laser. The first continuous infrared laser and the second continuous infrared laser are coupled and input to the waveguide module; The temperature of the waveguide module is controlled so that the difference frequency process of the first continuous infrared laser and the second continuous infrared laser in the waveguide module satisfies the phase matching condition. Under the phase-matching condition, the first continuous infrared laser and the second continuous infrared laser are made to have a difference frequency in the waveguide module to obtain a mid-infrared laser.

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