A frequency-modulated external cavity laser device

Abstract

The embodiment of the application discloses a frequency modulation external cavity laser device, which comprises a seed light source, a feedback loop external cavity, a light source frequency adjusting module, an FP cavity frequency adjusting module and an external cavity frequency adjusting module; the feedback loop external cavity comprises an FP cavity; the light source frequency adjusting module is used for adjusting the intrinsic frequency of the seed light beam; the FP cavity frequency adjusting module is used for adjusting the resonance frequency of the FP cavity; the external cavity frequency adjusting module is used for adjusting the resonance frequency of the feedback loop external cavity; the light source frequency adjusting module, the FP cavity frequency adjusting module and the external cavity frequency adjusting module are cooperatively modulated, so that the intrinsic frequency of the seed light beam, the resonance frequency of the FP cavity and the resonance frequency of the feedback loop external cavity satisfy the external cavity self-injection locking condition, and a frequency-locked laser is formed. The embodiment of the application solves the problem that the frequency modulation range of the existing narrow line width laser is small, can greatly improve the frequency modulation range, constructs a fast and wide range continuous frequency modulation external cavity narrow line width laser, and expands the application field of the laser device.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to laser technology, in particular to a frequency-modulated external cavity laser device. BACKGROUND

[0002] The line width of the laser and the quality factor of the laser cavity are directly related, and the quality factor of the semiconductor laser optical cavity is usually low due to material characteristics and process. The frequency-modulated single-frequency narrow line width laser has important applications in the fields of laser radar, optical frequency domain reflectometer, quantum, etc. At present, the laser device with frequency modulation usually uses an external cavity feedback method, one scheme of which is to use a grating to selectively feed back specific wavelength light to return the laser, and the other is to use an external mirror, and in order to avoid the multi-longitudinal mode effect of the long optical cavity, an interference filter is used to select a single longitudinal mode. The above two external cavity lasers can realize frequency modulation by rotating the grating or the interference filter. However, due to the low quality factor of the external cavity, the obtained laser line width is usually in the order of tens to hundreds of kilohertz, and a narrower line width cannot be obtained.

[0003] At present, various external cavity laser schemes using high-Q external cavities can achieve ultra-narrow line width, but the fast frequency modulation range is limited to hundreds of megahertz to gigahertz. In the fields of frequency-modulated continuous-wave laser radar and optical frequency domain reflectometer, the ranging accuracy is inversely proportional to the frequency modulation range, and in many quantum application fields, multiple absorption spectra of atoms are required, and a large range of frequency modulation of ultra-narrow line width laser is also required. The current laser device cannot meet the application requirements of these fields. SUMMARY

[0004] The present application provides a frequency-modulated external cavity laser device to realize a large range of high-speed continuous frequency modulation of the external cavity laser scheme through a high-Q FP optical cavity, obtain an ultra-narrow line width, and obtain a larger fast continuous frequency modulation range.

[0005] The embodiment of the present application provides a frequency-modulated external cavity laser device, which comprises a seed light source and a feedback loop external cavity, wherein the feedback loop external cavity comprises an FP cavity, and the cavity length of the FP cavity is less than or equal to 10 cm.

[0006] The seed light source is used to output a seed light beam.

[0007] The FP cavity is used to filter the seed light beam to form a transmitted light beam.

[0008] The feedback loop external cavity is used to feed back the transmitted light beam to the seed light source to form a feedback light path.

[0009] The frequency-modulated external cavity laser device further comprises a light source frequency adjustment module, an FP cavity frequency adjustment module and an external cavity frequency adjustment module.

[0010] The light source frequency adjustment module is configured to adjust the intrinsic frequency f1 of the seed light beam;

[0011] The FP cavity frequency adjustment module is configured to adjust the resonance frequency f2 of the FP cavity;

[0012] The external cavity frequency adjustment module is configured to adjust the resonance frequency f3 of the feedback loop external cavity;

[0013] The light source frequency adjustment module, the FP cavity frequency adjustment module and the external cavity frequency adjustment module are cooperatively modulated to make the intrinsic frequency f1 of the seed light beam, the resonance frequency f2 of the FP cavity and the resonance frequency f3 of the feedback loop external cavity satisfy the external cavity self-injection locking condition, and form a frequency-locked laser.

[0014] Optionally, the external cavity self-injection locking condition comprises:

[0015] The difference between the intrinsic frequency f1 of the seed light beam and the resonance frequency f2 of the FP cavity is less than the external cavity self-injection locking range of the feedback loop external cavity;

[0016] The difference between the resonance frequency f2 of the FP cavity and the resonance frequency f3 of the feedback loop external cavity is less than one half of the free spectral range of the feedback loop external cavity.

[0017] Optionally, the FP cavity frequency adjustment module and the external cavity frequency adjustment module are electrically controlled displacement modules; the electrically controlled displacement modules are respectively arranged on at least one optical component of the feedback loop external cavity and the FP cavity;

[0018] The electrically controlled displacement modules are configured to change the cavity length of the feedback loop external cavity or the FP cavity, or the electrically controlled displacement modules are configured to change the optical path of a light beam in the optical component to adjust the resonance frequency of the feedback loop external cavity or the FP cavity.

[0019] Optionally, the feedback loop external cavity and the FP cavity each comprise at least one reflecting unit, and the electrically controlled displacement modules are arranged on the reflecting units;

[0020] The electrically controlled displacement modules are configured to change the cavity length of the feedback loop external cavity or the FP cavity according to the formula Δf / f=ΔL / L to adjust the resonance frequency of the feedback loop external cavity or the FP cavity;

[0021] wherein f is the current resonance frequency of the feedback loop external cavity or the FP cavity, Δf is the change amount of the resonance frequency of the feedback loop external cavity or the FP cavity, L is the current cavity length of the feedback loop external cavity or the FP cavity, and ΔL is the change amount of the cavity length of the feedback loop external cavity or the FP cavity.

[0022] Optionally, the feedback loop external cavity and the FP cavity respectively comprise at least one prism unit, and the electrically controlled displacement module is arranged on the prism unit.

[0023] The electrically controlled displacement module is configured to change the optical path of the light beam in the optical assembly according to a formula Δf / f=n1*ΔL / (n2*L) to adjust the resonant frequency of the feedback loop external cavity or the FP cavity.

[0024] Wherein, f is the current resonant frequency of the feedback loop external cavity or the FP cavity, Δf is the change amount of the resonant frequency of the feedback loop external cavity or the FP cavity, n2*L is the total optical path of the feedback loop external cavity or the FP cavity, and n1*ΔL is the change amount of the optical path of the feedback loop external cavity or the FP cavity.

[0025] Optionally, the FP cavity frequency adjustment module and the external cavity frequency adjustment module are respectively an electrically controlled refractive index module or a thermally controlled refractive index module; the electrically controlled refractive index module or the thermally controlled refractive index module is located in the feedback loop external cavity or the FP cavity, respectively.

[0026] The electrically controlled refractive index module is configured to change the refractive index through the electro-optic effect, and the thermally controlled refractive index module is configured to change the refractive index through the thermo-optic effect to adjust the optical path of the light beam in the electrically controlled refractive index module or the thermally controlled refractive index module, thereby adjusting the resonant frequency of the feedback loop external cavity or the FP cavity.

[0027] Optionally, the seed light source comprises a first end and a second end; the seed light beam is output from the first end of the seed light source, and the transmitted light beam is input from the first end of the seed light source.

[0028] The feedback loop external cavity further comprises a first collimating unit, a unidirectional transmission unit and a reflecting unit.

[0029] The first collimating unit is configured to collimate the seed light beam.

[0030] The unidirectional transmission unit is configured to transmit the seed light beam to the FP cavity and block the reflected light beam of the FP cavity from being incident on the seed light source.

[0031] The reflecting unit is configured to reflect the transmitted light beam of the FP cavity back to the seed light source to form a feedback light path.

[0032] Optionally, the first collimating unit comprises a first lens, the unidirectional transmission unit comprises a polarization beamsplitter, a first quarter-wave plate, a second quarter-wave plate and a second lens in sequence, and the reflecting unit comprises a first mirror.

[0033] The FP cavity is located between the first quarter-wave plate and the second quarter-wave plate; and the second lens is located between the FP cavity and the second quarter-wave plate or between the second quarter-wave plate and the first mirror.

[0034] Optionally, the seed light source comprises a first end and a second end; the seed light beam is output from the first end of the seed light source, and the transmitted light beam is input from the first end of the seed light source; or the seed light beam is output from the first end of the seed light source, and the transmitted light beam is input from the second end of the seed light source.

[0035] The feedback loop external cavity further comprises a unidirectional transmission unit and a light ray turning unit.

[0036] The unidirectional transmission unit is configured to transmit the seed light beam to the FP cavity and block the reflected light beam of the FP cavity from being incident on the seed light source.

[0037] The light ray turning unit is configured to change the transmission direction of the transmitted light beam of the FP cavity so that the transmitted light beam is fed back to the seed light source to form a feedback light path.

[0038] Optionally, the unidirectional transmission unit comprises a circulator, and the light ray turning unit comprises a second mirror, a third mirror and a fourth mirror.

[0039] The beam transmission path in the frequency-modulated external cavity laser device is as follows:

[0040] The seed light beam is output from the first end of the seed light source, input from the first end of the circulator, and then output from the second end of the circulator to be incident on the FP cavity to form the transmitted light beam; the transmitted light beam is reflected by the second mirror, the third mirror and the fourth mirror in sequence and then incident on the third end of the circulator and output from the first end of the circulator to be fed back to the seed light source.

[0041] Optionally, the unidirectional transmission unit comprises an isolator, and the light ray turning unit comprises a fifth mirror, a sixth mirror, a seventh mirror and an eighth mirror.

[0042] The beam transmission path in the frequency-modulated external cavity laser device is as follows:

[0043] The seed light beam is output from the first end of the seed light source, input from the first end of the isolator, and then output from the second end of the isolator to be incident on the FP cavity to form the transmitted light beam; the transmitted light beam is reflected by the fifth mirror, the sixth mirror, the seventh mirror and the eighth mirror in sequence and then incident on the second end of the seed light source.

[0044] Optionally, the unidirectional transmission unit further comprises at least one isolator, and the at least one isolator is located between the seed light source and the FP cavity.

[0045] Optionally, the FP cavity comprises a ninth mirror and a tenth mirror which are parallel to each other, and the seed light beam is incident by the ninth mirror and is emitted by the tenth mirror.

[0046] Alternatively, the FP cavity comprises an eleventh mirror, a twelfth mirror and a thirteenth mirror, and the seed light beam is incident by the eleventh mirror, is reflected by the twelfth mirror and the thirteenth mirror in turn, and is emitted by the eleventh mirror.

[0047] Optionally, the seed light source comprises a semiconductor laser; or the seed light source comprises a combination of a gain chip and a filter, and the filter is located at any position of the feedback loop out-cavity.

[0048] In the embodiment of the present application, the seed light source and the feedback loop out-cavity are arranged, and the short FP cavity with a cavity length less than or equal to two centimeters is arranged in the feedback loop out-cavity, the seed light source is used to emit the seed light beam, the high-Q FP cavity is used to filter the seed light beam to form the transmission light beam, and the feedback loop out-cavity is used to feed back the transmission light beam to the seed light source to form the feedback light path, so that the frequency-locked laser with ultra-narrow linewidth is realized. In addition, three frequency adjustment modules are arranged in the embodiment to cooperatively modulate the frequencies of the three optical cavities, so that the frequencies of the three optical cavities meet the self-injection locking condition of the out-cavity, the frequency-locked laser is formed, and the ultra-large range high-speed continuous frequency modulation is realized. The embodiment of the present application solves the problem that the frequency modulation range of the existing narrow linewidth laser is small, the high-Q FP short cavity is used to participate in the frequency locking of the feedback out-cavity, and the frequencies of the three optical cavities in the frequency modulation out-cavity laser device are cooperatively modulated, so that the frequency modulation range can be increased to tens to hundreds of GHz, the fast large-range continuous frequency modulation out-cavity narrow linewidth laser is constructed, the frequency modulation out-cavity laser device can improve the ranging accuracy in the fields of continuous wave frequency modulation laser radar, optical frequency domain reflectometer and the like, and for the quantum application field, the frequency modulation out-cavity laser of the present application can meet the requirement of using multiple absorption spectra of atoms, so as to expand the application field of the laser device. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 and Figure 2 are the simplified structure schematic diagrams of two frequency modulation out-cavity laser devices provided by the embodiment of the present application;

[0050] Figure 3 and Figure 4 are the frequency spectrum diagrams of the optical cavities in Figure 1 and Figure 2 , respectively.

[0051] Figure 5is a structural schematic diagram of still another frequency-modulated external cavity laser device provided by an embodiment of the present application;

[0052] Figure 6 is a structural schematic diagram of still another frequency-modulated external cavity laser device provided by an embodiment of the present application;

[0053] Figure 7 and Figure 8 are structural schematic diagrams of still two frequency-modulated external cavity laser devices provided by an embodiment of the present application;

[0054] Figure 9 is a structural schematic diagram of still another frequency-modulated external cavity laser device provided by an embodiment of the present application;

[0055] Figure 10 is a structural schematic diagram of still another frequency-modulated external cavity laser device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0056] The terms used in the embodiments of the present application are merely for the purpose of describing particular embodiments and are not intended to limit the present application. It should be noted that the positional words such as "upper", "lower", "left", "right", and the like described in the embodiments of the present application are described with the angle shown in the drawings, and should not be understood as a limitation on the embodiments of the present application. In addition, it should be understood in the context that when referring to one element being formed "on" or "under" another element, it can be directly formed "on" or "under" another element, or indirectly formed "on" or "under" another element through an intermediate element. The terms "first", "second", and the like are only for the purpose of description and do not represent any order, quantity or importance, but are only used to distinguish different components. The above terms in the present application can be understood according to the specific meaning according to the specific circumstances for those skilled in the art.

[0057] As described in the background section, in recent years, various external cavity schemes using high-Q optical cavities have appeared, which can obtain ultra-narrow linewidth lasers below kilohertz, such as using a high-quality factor whispering gallery optical cavity as a filter to construct a compound optical cavity, which can realize a laser with a linewidth of hundreds of hertz or even hertz, but its fast tuning range using a piezoelectric ceramic is only hundreds of megahertz; or using an on-chip ring cavity, which can achieve a static thermal tuning range of 9 GHz, but the piezoelectric ceramic fast tuning is only 1 GHz @ 12 kHz modulation frequency; in addition, there are also laser schemes using fiber optical cavities or high-Q FP optical cavities, but their fast tuning ranges are also small.

[0058] Therefore, the embodiments of the present application provide a frequency-modulated external cavity laser device. Figure 1 and Figure 2 are simplified structural schematic diagrams of two frequency-modulated external cavity laser devices provided by an embodiment of the present application, for referenceFigure 1 and Figure 2 The frequency-modulated external cavity laser device comprises a seed light source 10 and a feedback loop external cavity 30, the feedback loop external cavity 30 comprises an FP cavity 20, and the cavity length of the FP cavity 20 is less than or equal to 10 cm. The seed light source 10 is used to output a seed light beam; the FP cavity 20 is used to filter the seed light beam to form a transmitted light beam; and the feedback loop external cavity 30 is used to feed back the transmitted light beam to the seed light source 10 to form a feedback light path.

[0059] The frequency-modulated external cavity laser device further comprises a light source frequency adjustment module, an external cavity frequency adjustment module and an FP cavity frequency adjustment module (not shown in the figure); the light source frequency adjustment module is used to adjust the intrinsic frequency f1 of the seed light beam; the external cavity frequency adjustment module is used to adjust the resonant frequency f3 of the feedback loop external cavity; and the FP cavity frequency adjustment module is used to adjust the resonant frequency f2 of the FP cavity; the light source frequency adjustment module, the FP cavity frequency adjustment module and the external cavity frequency adjustment module are coordinated to modulate, so that the intrinsic frequency f1 of the seed light beam, the resonant frequency f2 of the FP cavity and the resonant frequency f3 of the feedback loop external cavity satisfy the external cavity self-injection locking condition, and a frequency-locked laser is formed.

[0060] The seed light source 10 essentially belongs to an optical cavity with gain, and can be a semiconductor laser, can generate a seed light beam with a relatively wide line width, or can be a combination of a gain chip and a filter. The gain chip has a relatively high gain for a specific waveband (for example, a C waveband), and the filter can select a laser wavelength within the gain spectrum (several tens of nm) of the gain chip. The feedback loop external cavity 30 is used to form external cavity self-injection locking of the seed light beam. The feedback loop external cavity 30 essentially is a low-Q optical cavity, which can reduce the laser line width to a certain extent. The feedback loop external cavity 30 can be a coaxial optical cavity that returns along the original path, or can be a feedback loop formed by a turning assembly, for example, a ring-shaped feedback loop. In the embodiment of the present application, the FP cavity 20 is arranged in the feedback loop external cavity 30. The FP cavity 20 essentially is a high-Q optical cavity. The filtered feedback laser through the FP cavity 20 can form external cavity self-injection locking, and can also narrow the original line width of the laser.

[0061] It should be noted that the cavity length of the FP cavity 20 arranged in the present application is less than or equal to 10 cm. Essentially, a short FP cavity is used. On the premise of using a high Q value to achieve an ultra-narrow line width laser, the FP cavity is used to realize rapid and large-range frequency modulation. Compared with other solid optical cavities, the use of a short FP cavity can expand the modulation range, and the modulation range can be improved by several orders of magnitude. For example, when a 2 mm long FP short cavity is used, the cavity mirror reflectivity is greater than 99.992%, and the Q value is greater than 10 8By changing the cavity length by 2 μm, one-thousandth of the FP cavity length can be altered. This results in a change of approximately 200 GHz in the optical cavity frequency around 1550 nm (corresponding to an optical frequency of 200 THz). Compared to high-Q external cavity lasers such as fiber lasers, whispering-gallery cavities, and on-chip micro-ring cavities, the frequency modulation range of this embodiment can be improved by one to two orders of magnitude. For example, when the FP cavity length is 2 cm, changing the cavity length by 2 μm (one-ten-thousandth of the cavity length) can achieve a wide frequency modulation range of 20 GHz @ 1550 nm. This also significantly improves the modulation range compared to existing high-Q external cavity lasers.

[0062] This invention essentially employs three optical cavities to form a composite external cavity laser. A necessary condition for effective external cavity self-injection locking is that the frequencies of the three optical cavities must be aligned as closely as possible. Therefore, it can be understood that during frequency modulation, the external cavity laser device in this embodiment requires coordinated modulation of the three optical cavities to ensure that their frequencies always meet the external cavity self-injection locking condition, thereby dynamically forming a frequency-locked laser. Specifically, this invention includes a light source frequency adjustment module, an FP cavity frequency adjustment module, and an external cavity frequency adjustment module, which are used to synchronously or proportionally adjust the frequencies of the three optical cavities to ensure frequency alignment, thus maintaining the external cavity self-injection locking condition during dynamic frequency modulation and forming a frequency-locked laser. Figure 3 and Figure 4 They are respectively Figure 1 and Figure 2 The spectrum of the optical cavity, as shown below Figure 3 and Figure 4 As shown, the vertical black solid line represents the intrinsic frequency f1 of the seed source; the narrower periodic dashed line represents the transmission spectrum of the FP cavity, and its transmission peak frequency close to the intrinsic frequency f1 of the seed source is the resonant frequency f2 of the FP cavity; the wider Lorentz-shaped solid line represents the transmission spectrum of the external cavity of the feedback loop, and its transmission peak frequency close to the intrinsic frequency f1 of the seed source is the resonant frequency f3 of the external cavity of the feedback loop. To ensure effective self-injection locking of the three optical cavities, the intrinsic frequency f1 of the seed source, the transmission peak frequency f2 of the FP cavity, and the transmission peak frequency f3 of the external cavity of the feedback loop need to be kept as aligned as possible in the spectrum. When the frequency-modulated external cavity laser device is frequency-modulated, for example, when the resonant frequency of the FP cavity changes (i.e., when the narrower periodic dashed line moves left and right), in order to maintain effective self-injection locking, the transmission peak frequency f3 of the external cavity of the feedback loop and the intrinsic frequency f1 of the seed source must move synchronously with the transmission peak frequency f2 of the FP cavity. That is, it is necessary to ensure the coordinated modulation of the three optical cavities to avoid loss of self-injection locking and mode hopping.

[0063] It should be noted that the three frequency adjustment modules can be controlled by the same control device to realize the cooperative modulation of the three optical cavities. Those skilled in the art can design according to the actual situation, and this is not limited here. In addition, the three frequency adjustment modules can be additional frequency adjustment structures. For example, for the FP cavity, the corresponding frequency adjustment module can be a piezoelectric ceramic PZT, which can adjust the resonant frequency by changing the FP cavity length. The frequency adjustment module can also be a frequency adjustment component of the seed light source 10, the feedback loop external cavity 30 and the FP cavity 20. Taking the seed light source 10 as an example, the seed light source 10 is a DFB distributed feedback laser, which has a frequency adjustment component Bragg grating. The frequency of the distributed feedback laser can be adjusted by changing the current injected into the DFB and using the Bragg grating.

[0064] In the embodiment of the present application, a seed light source and a feedback loop external cavity are provided, and a short FP cavity with a cavity length less than or equal to two centimeters is arranged in the feedback loop external cavity. The seed light source emits a seed light beam, the FP cavity with a high Q value filters the seed light beam to form a transmitted light beam, and the feedback loop external cavity feeds back the transmitted light beam to the seed light source to form a feedback light path, thereby realizing a frequency-locked laser with an ultra-narrow linewidth. In addition, three frequency adjustment modules are provided in the embodiment to cooperatively modulate the frequencies of the three optical cavities, so as to ensure that the frequencies of the three optical cavities meet the external cavity self-injection locking condition and form a frequency-locked laser, thereby realizing a super-large range high-speed continuous frequency modulation. The embodiment of the present application solves the problem of small frequency modulation range of the existing narrow linewidth laser. The high Q value FP short cavity is used to participate in the frequency locking of the feedback external cavity, and the frequencies of the three optical cavities in the frequency modulation external cavity laser device are cooperatively modulated, so as to increase the frequency modulation range to tens to hundreds of GHz, construct a fast and large range continuous frequency modulation external cavity narrow linewidth laser, and improve the ranging accuracy of the frequency modulation continuous wave laser radar, optical frequency domain reflectometer and other fields. At the same time, for the quantum application field, the frequency modulation external cavity laser of the present application can meet the requirement of using multiple atomic absorption spectra, thereby expanding the application field of the laser device.

[0065] For the specific conditions of the frequency cooperative modulation of the above three optical cavities, the embodiment of the present application provides a detailed scheme. Continue to refer to Figures 1-4 The further optional external cavity self-injection locking condition includes that the difference between the intrinsic frequency f1 of the seed light beam and the resonant frequency f2 of the FP cavity is less than the external cavity self-injection locking range of the feedback loop external cavity, and the difference between the resonant frequency f2 of the FP cavity and the resonant frequency f3 of the feedback loop external cavity is greater than or equal to one half of the free spectral range of the feedback loop external cavity.

[0066] Wherein, for the resonance frequency f2 of the FP cavity and the resonance frequency f3 of the external cavity of the feedback loop, it can be seen from the spectrum that the difference should not exceed half of the free spectral range FSR3 of the external cavity of the feedback loop. At this time, the resonance frequency f2 is located in the free spectral range FSR3 of the external cavity of the feedback loop, which means that the resonance frequency f2 of the FP cavity and the resonance frequency f3 of the external cavity of the feedback loop can be substantially aligned. As for the intrinsic frequency f1 of the seed light beam and the resonance frequency f2 of the FP cavity, for example, in a conventional distributed feedback laser chip, under appropriate feedback conditions, the external cavity self-injection locking range is several hundred megahertz to several gigahertz. In order to ensure self-injection locking, the difference between the intrinsic frequency f1 of the seed light beam and the resonance frequency f2 of the FP cavity should be less than the above-mentioned external cavity self-injection locking range. At this time, the position of the intrinsic frequency f1 of the seed light beam on the spectrum is close to the resonance frequency f2. Based on the above-mentioned frequencies f1, f2 and f3 being able to be close to or within the alignment range on the spectrum during the dynamic frequency tuning, the external cavity self-injection locking condition can be met, and the frequency-locked laser can be formed.

[0067] On the basis of the above, the embodiment of the present application also provides a plurality of ways to adjust the frequency of the optical cavity. Specifically, the FP cavity frequency adjustment module and the external cavity frequency adjustment module are electrically controlled displacement modules; the electrically controlled displacement modules are respectively arranged on at least one optical component of the external cavity of the feedback loop and the FP cavity; the electrically controlled displacement modules are used to change the cavity length of the external cavity of the feedback loop or the FP cavity, or the electrically controlled displacement modules are used to change the optical path of the light beam in the optical component, so as to adjust the resonance frequency of the external cavity of the feedback loop or the FP cavity.

[0068] In addition, the FP cavity frequency adjustment module and the external cavity frequency adjustment module can also be electrically controlled refractive index modules or thermally controlled refractive index modules; the electrically controlled refractive index modules or the thermally controlled refractive index modules are respectively located in the external cavity of the feedback loop or the FP cavity; the electrically controlled refractive index modules are used to change the refractive index through the electro-optic effect, and the thermally controlled refractive index modules are used to change the refractive index through the thermo-optic effect, so as to adjust the optical path of the light beam in the electrically controlled refractive index module or the thermally controlled refractive index module, thereby adjusting the resonance frequency of the external cavity of the feedback loop or the FP cavity.

[0069] First, the scheme of adjusting the frequency of the optical cavity by the electrically controlled displacement module is introduced in detail. Figure 5 is another structure diagram of the frequency-adjusted external cavity laser device provided by the embodiment of the present application, referring to Figure 5The feedback loop outer cavity 30 and the FP cavity 20 respectively comprise at least one reflecting unit, and the electrically-controlled displacement module 40 is arranged on the reflecting unit; the electrically-controlled displacement module 40 is used to change the cavity length of the feedback loop outer cavity 30 or the FP cavity 20 according to the formula Δf / f=ΔL / L, so as to adjust the resonant frequency of the feedback loop outer cavity 30 or the FP cavity 20; wherein f is the current resonant frequency of the feedback loop outer cavity 30 or the FP cavity 20, Δf is the change amount of the resonant frequency of the feedback loop outer cavity 30 or the FP cavity 20, L is the current cavity length of the feedback loop outer cavity 30 or the FP cavity 20, and ΔL is the change amount of the cavity length of the feedback loop outer cavity 30 or the FP cavity 20.

[0070] It should be noted that the scheme of adjusting the optical cavity frequency by the electrically-controlled displacement module can be applied to different composite external cavity laser structures. Figure 5 For example, as shown in the composite external cavity laser structure, in this embodiment, the seed light source 10 comprises a first end 1 and a second end 2; the seed light beam is output from the first end 1 of the seed light source 10, and the transmitted light beam is input from the first end 1 of the seed light source 10; the feedback loop outer cavity 30 further comprises a first collimating unit 31, a unidirectional transmission unit 32 and a reflecting unit 33; the first collimating unit 31 is used to collimate the seed light beam; the unidirectional transmission unit 32 is used to transmit the seed light beam to the FP cavity 20 and block the reflected light beam of the FP cavity 20 from being incident on the seed light source 10; and the reflecting unit 33 is used to reflect the transmitted light beam of the FP cavity 20 back to the seed light source 10 to form a feedback light path.

[0071] More specifically, the first collimating unit 31 can comprise a first lens 311, the unidirectional transmission unit 32 can comprise, in sequence, a polarization beamsplitter 321, a first quarter-wave plate 322, a second quarter-wave plate 323 and a second lens 324, and the reflecting unit 33 can comprise a first mirror 331; the FP cavity 20 is located between the first quarter-wave plate 322 and the second quarter-wave plate 323, and the second lens 324 is located between the FP cavity 20 and the second quarter-wave plate 323.

[0072] The FP cavity can be a hollow FP cavity or a solid FP cavity. The hollow FP cavity can be a parallel cavity, a plano-concave cavity or a concave-concave cavity. Specifically, the FP cavity 20 can be arranged to comprise a ninth mirror 21 and a tenth mirror 22 which are parallel to each other, and the seed light beam is incident by the ninth mirror 21 and is emitted by the tenth mirror 22.

[0073] In the frequency-modulated external cavity laser device, the feedback light path is specifically as follows: the seed light source 10 emits a seed light beam, which is collimated by the first lens 311 and then passes through a polarization beam splitter 321. The polarization beam splitter 321 transmits the P parallel polarization component of the seed light beam and reflects the S vertical polarization component. The P parallel polarization component is converted into circularly polarized light after passing through a first quarter-wave plate 322, is coupled out of the FP cavity, is collimated by a second lens 324, and is then converted into first linearly polarized light by a second quarter-wave plate 323. The polarization direction of the first linearly polarized light is perpendicular to that of the P parallel polarization component. The first linearly polarized light is reflected by a first mirror 331 and then converted into circularly polarized light by the second quarter-wave plate 323, passes through the FP cavity, and is then converted into second linearly polarized light by the first quarter-wave plate 322. The polarization direction of the second linearly polarized light is the same as that of the P parallel polarization component. At this time, the second linearly polarized light can pass through the polarization beam splitter 321, and finally returns to the seed light source 10 through the first lens 311.

[0074] It should be noted that the polarization beam splitter 321, the first quarter-wave plate 322, the second quarter-wave plate 323, and the second lens 324 substantially constitute a one-way transmission unit 32, which can be used to block the light beam reflected by the FP cavity and ensure that the light beam in the feedback loop external cavity returns to the original route coaxially. Specifically, it can be understood that the circularly polarized light converted by the first quarter-wave plate 322 will form reflected light toward the seed light source 10 on the reflection structure in the FP cavity 20 when passing through the FP cavity 20. If the reflected light directly enters the seed light source 10, it will affect the self-injection locking of the entire external cavity. In the structure of the present embodiment, the first quarter-wave plate 322 and the polarization beam splitter 321 are arranged such that the reflected light will form third linearly polarized light after passing through the first quarter-wave plate 322. The polarization direction of the third linearly polarized light is perpendicular to that of the P parallel polarization component. At this time, the third linearly polarized light is reflected by the polarization beam splitter 321 and cannot pass through the polarization beam splitter 321, thereby effectively blocking the reflected light formed by the FP cavity from being fed back to the seed light source.

[0075] In this embodiment, the feedback loop outer cavity 30 corresponds to the first electrically controlled displacement module 41, which can be installed on the back of the reflection unit 33, i.e., the first mirror 331, and can also be installed on the side or front of the first mirror 331. The electrically controlled displacement module 40 can be a piezoelectric ceramic PZT or a voice coil motor. Those skilled in the art can understand that the piezoelectric ceramic PZT or the voice coil motor can accurately move the position of the reflection unit 33 under the control of an electric signal, thereby adjusting the cavity length of the feedback loop outer cavity 30. In other words, the resonant frequency f3 of the feedback loop outer cavity 30 can be adjusted by changing the cavity length through the first electrically controlled displacement module 41. Similarly, for the FP cavity 20, the corresponding electrically controlled displacement module 40 is the second electrically controlled displacement module 42, which can also be a piezoelectric ceramic PZT or a voice coil motor. As shown in the figure, the second electrically controlled displacement module 42 can be arranged on the back of the tenth mirror 22, or can also be installed on the side or front of the tenth mirror 22. Similarly, by accurately moving the position of the tenth mirror 22 through the piezoelectric ceramic PZT or the voice coil motor, the resonant frequency f2 of the FP cavity 20 can be adjusted.

[0076] In this embodiment, the electrically controlled displacement module 40 is mainly responsible for moving the position of a component of the optical cavity, thereby adjusting the cavity length of the optical cavity, and changing the frequency of the optical cavity by changing the cavity length. Therefore, when adjusting the cavity length of the optical cavity, it is necessary to ensure that the frequencies of the three optical cavities are adjusted in coordination. Specifically, the cavity length of the feedback loop outer cavity 30 or the FP cavity 20 can be changed according to the ratio of the cavity length change amount to the current cavity length, and the ratio of the frequency change amount to the current frequency, to guide the adjustment of the resonant frequency of the feedback loop outer cavity 30 or the FP cavity 20.

[0077] Figure 6 is another structure diagram of a frequency-adjusted external cavity laser device provided by an embodiment of the present application, which is compared with Figure 5 and Figure 6 The second lens 324 in the optional one-way transmission unit 32 is located between the second quarter-wave plate 323 and the first mirror 331. As shown in Figure 6 , the frequency-adjusted external cavity laser device is essentially a variant of Figure 5 . In the structure of the laser device shown in Figure 6 , the transmitted light of the FP cavity 20 converges on the first mirror 331 through the second lens 324, thereby reducing the accuracy and difficulty of angle alignment of the first mirror 331.

[0078] The present embodiment provides other composite external cavity laser structures for the scheme of adjusting the frequency of the optical cavity by the electrically controlled displacement module. Figure 7 and Figure 8 are two other structure diagrams of frequency-adjusted external cavity laser devices provided by an embodiment of the present application, which are compared with Figure 7 and Figure 8In the two embodiments, the seed light source 10 comprises a first end 1 and a second end 2; the seed light beam is output from the first end 1 of the seed light source 10, and the transmitted light beam is input from the first end 1 of the seed light source 10; or the seed light beam is output from the first end 1 of the seed light source 10, and the transmitted light beam is input from the second end 2 of the seed light source 10; the feedback loop external cavity 30 further comprises a one-way transmission unit 32 and a light ray turning unit 35; the one-way transmission unit 32 is used for transmitting the seed light beam to the FP cavity 20 and blocking the reflected light beam of the FP cavity 20 from being incident on the seed light source 10; and the light ray turning unit 35 is used for changing the transmission direction of the transmitted light beam of the FP cavity 20 so as to form a feedback light path by feeding back the transmitted light beam to the seed light source 10.

[0079] Specifically, referring to Figure 7 In this embodiment, the seed light beam is output from the first end 1 of the seed light source 10, and the transmitted light beam is input from the first end 1 of the seed light source 10. The one-way transmission unit 32 comprises a circulator 325, and the light ray turning unit 35 comprises a second mirror 351, a third mirror 352 and a fourth mirror 353. The light beam transmission path in the frequency-modulated external cavity laser device is as follows: the seed light beam is output from the first end 1 of the seed light source 10, input from the first end 1 of the circulator 325, output from the second end 2 of the circulator 325, incident on the FP cavity 20 to form a transmitted light beam; the transmitted light beam is reflected by the second mirror 351, the third mirror 352 and the fourth mirror 353 in sequence, incident on the third end 3 of the circulator 325 and output from the first end 1 of the circulator 325 to be fed back to the seed light source 10.

[0080] Referring to Figure 8 In this embodiment, the seed light beam is output from the first end 1 of the seed light source 10, and the transmitted light beam is input from the second end 2 of the seed light source 10. The one-way transmission unit 32 comprises an isolator 326, and the light ray turning unit 35 comprises a fifth mirror 354, a sixth mirror 355, a seventh mirror 356 and an eighth mirror 357. The light beam transmission path in the frequency-modulated external cavity laser device is as follows: the seed light beam is output from the first end 1 of the seed light source 10, input from the first end 1 of the isolator 326, output from the second end 2 of the isolator, incident on the FP cavity to form a transmitted light beam; the transmitted light beam is reflected by the fifth mirror 354, the sixth mirror 355, the seventh mirror 356 and the eighth mirror 357 in sequence, and then incident on the second end 2 of the seed light source 10.

[0081] In Figure 7 and Figure 8In the two embodiments shown, the first electrically controlled displacement module 41 corresponding to the feedback loop outer cavity 30 can be installed on the back of any one of the mirrors in the light turning unit 35. By adjusting the position of the mirror, the cavity length of the feedback loop outer cavity 30 can be changed, thereby adjusting the frequency of the optical cavity. For the FP cavity 20, the second electrically controlled displacement module 42 can be arranged on the back of the tenth mirror 22. By precisely moving the position of the tenth mirror 22 through a piezoelectric ceramic PZT or a voice coil motor, the resonant frequency f2 of the FP cavity 20 can be adjusted.

[0082] In addition, for the Figures 5-8 In the composite outer cavity laser structure provided in the four embodiments, at least one isolator can be additionally arranged in the unidirectional transmission unit as described above, and the isolator is located between the seed light source and the FP cavity. At this time, the isolator can further block the reflected light of the FP cavity, thereby effectively reducing the influence of the direct reflected light of the FP cavity on the entire outer cavity frequency locking.

[0083] Figure 9 is another structure diagram of a frequency-modulated outer cavity laser device provided by an embodiment of the present application, referring to Figure 9 This embodiment provides another implementation for the structure of the FP cavity. As shown in Figure 9 The FP cavity 20 can include an eleventh mirror 23, a twelfth mirror 24, and a thirteenth mirror 25. The seed light beam is incident from the eleventh mirror 23, and is reflected by the twelfth mirror 24 and the thirteenth mirror 25 in turn before being emitted from the eleventh mirror 23.

[0084] In this embodiment, the FP cavity 20 is essentially a ring-shaped FP cavity composed of three high-reflectivity mirrors. The cavity length modulation of the ring-shaped FP cavity is realized through a piezoelectric ceramic PZT on one of the mirrors. The seed light beam is coupled into the ring-shaped FP cavity 20 through a mirror arranged in the feedback loop outer cavity. After the seed light beam passes through the eleventh mirror 23, it is reflected by the twelfth mirror 24, the eleventh mirror 23, the thirteenth mirror 25, the eleventh mirror 23, and the twelfth mirror 24 in turn before being emitted from the eleventh mirror 23, forming a transmitted light beam. The transmitted light beam returns to the seed light source 10 along the original path. The cavity length of the feedback loop outer cavity is realized through a piezoelectric ceramic PZT arranged on a mirror in the feedback loop outer cavity, which will not be described here.

[0085] In the frequency-modulated outer cavity laser device of each of the above embodiments, in addition to the deformation of the feedback loop outer cavity and the FP cavity, the seed light source can also be implemented in different ways. For example, Figures 5-9 As shown in the embodiment, the seed light source 10 can be a semiconductor laser 11; or the seed light source 10 can be arranged to include a combination of a gain chip 12 and a filter 13, and the filter 13 can be arranged at any position of the feedback loop outer cavity 30.

[0086] Furthermore, those skilled in the art will understand that the frequency-locked lasers of the aforementioned frequency-modulated external cavity laser devices have different output modes, such as... Figure 5 and Figure 6 As shown, the frequency-locked laser can be reflected upwards by the polarization beam splitter 321, as... Figure 9 and Figure 10 The laser device shown can output frequency-locked laser light from the ring FP cavity 20. And for... Figure 7 The laser device shown can optionally have a beam splitter placed in the optical path between the third reflecting mirror 352 and the fourth reflecting mirror 353, using the beam splitter to output the frequency-locked laser. Similarly, for Figure 8 The laser device shown can optionally have a beam splitter placed in the optical path between the sixth reflector 355 and the seventh reflector 356, and the frequency-locked laser output can be generated by the beam splitter.

[0087] In other embodiments of the present invention, an electrically controlled displacement module can be used to achieve optical cavity frequency adjustment based on different principles. Figure 10 This is a schematic diagram of another frequency-modulated external cavity laser device provided in an embodiment of the present invention, for reference. Figure 10 In this embodiment, the feedback loop external cavity 30 and / or the FP cavity 20 each include at least one prism unit 50, and an electrically controlled displacement module 40 is mounted on the prism unit 50. The electrically controlled displacement module 40 is used to change the optical path of the beam in the optical component according to the formula Δf / f=n1*ΔL / (n2*L) to adjust the resonant frequency of the feedback loop external cavity 30 or the FP cavity 20. At this time, f is the current resonant frequency of the feedback loop external cavity or the FP cavity, Δf is the change in the resonant frequency of the feedback loop external cavity or the FP cavity, n2*L is the total optical path of the feedback loop external cavity or the FP cavity, and n1*ΔL is the change in the optical path of the feedback loop external cavity or the FP cavity.

[0088] In this embodiment, a prism unit 50 is provided in the outer cavity 30 of the feedback loop and / or the FP cavity 20, so that the seed beam has a partial optical path within the prism unit 50. Since the prism unit 50 has a certain refractive index n1, the position of the prism unit 50 can be adjusted by an electrically controlled displacement module 40 such as a piezoelectric ceramic PZT or a voice coil motor. Conversely, the relative position of the beam within the prism unit 50 can be adjusted, thereby changing the optical path of the beam within the prism unit 50. The optical path within the prism unit 50 can be represented by n1*L. When the prism unit 50 moves in a direction perpendicular to the beam, the path length L and the optical path n1*L within the prism unit 50 can be changed. In this embodiment, the cavity length of the outer cavity 30 of the feedback loop or the FP cavity 20 can also be changed based on the fact that the ratio of the change in optical path to the current optical path is equal to the ratio of the change in frequency to the current frequency, thereby guiding the adjustment of the resonant frequency of the outer cavity 30 of the feedback loop or the FP cavity 20. As shown in the figure, the electrically controlled displacement module 40 can be installed on the side of the prism unit 50. Those skilled in the art can also set it in any other location according to the actual design, and there are no restrictions here.

[0089] It should be noted that, as Figure 10 The FP cavity and feedback loop external cavity structures shown are only one implementation method; those skilled in the art can refer to them. Figures 5-9 The composite external cavity structure shown involves reasonable modifications to the FP cavity and the feedback loop external cavity, which will not be elaborated further here. It should also be noted that since the optical path length of the optical cavity is essentially linearly related to the phase (θ = 2πL / λ), using the optical path length as an adjustment factor in the above embodiments is merely a descriptive method. Those skilled in the art will understand that the phase of the optical cavity can also be adjusted using the aforementioned prism unit and electrically controlled displacement module. Therefore, designs by those skilled in the art to adjust the frequency of the optical cavity by changing the phase based on the above embodiments are essentially the same as adjusting the frequency of the optical cavity by changing the optical path length in the embodiments of this invention. These are reasonable modifications based on the above embodiments and therefore do not depart from the protection scope of this invention.

[0090] Regarding the scheme for adjusting the optical cavity frequency using an electrically controlled refractive index module or a thermally controlled refractive index module provided in the embodiments of the present invention, based on the above-described prism unit and electrically controlled displacement module scheme, those skilled in the art will understand that the optical path change of the optical cavity depends not only on the path L of the beam in the optical component, but also on the refractive index n of the optical component. Based on this, in the embodiments of the present invention, the electro-optic effect or the thermo-optic effect can be utilized to respectively set corresponding electrically controlled refractive index modules and thermally controlled refractive index modules in the feedback loop outer cavity or the FP cavity. The electrically controlled refractive index module or thermally controlled refractive index module changes the optical path by varying the refractive index, thereby adjusting the resonant frequency of the feedback loop outer cavity and the FP cavity. It is understood that the composite outer cavity structure provided in the above embodiments can also be used to adjust the optical cavity frequency using an electrically controlled refractive index module or a thermally controlled refractive index module. Those skilled in the art can design according to actual conditions, and examples will not be provided here.

[0091] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A frequency-modulated external cavity laser device, characterized in that, It includes a seed light source and a feedback loop outer cavity, wherein the feedback loop outer cavity includes an FP cavity, and the length of the FP cavity is less than or equal to 10cm; The seed light source is used to output a seed beam; The FP cavity is used to filter the seed beam to form a transmitted beam; The external cavity of the feedback loop is used to feed the transmitted beam back to the seed light source to form a feedback optical path; The frequency-modulated external cavity laser device also includes a light source frequency adjustment module, an FP cavity frequency adjustment module, and an external cavity frequency adjustment module; The light source frequency adjustment module is used to adjust the intrinsic frequency f1 of the seed beam; The FP cavity frequency adjustment module is used to adjust the resonant frequency f2 of the FP cavity; The external cavity frequency adjustment module is used to adjust the resonant frequency f3 of the external cavity of the feedback loop; The light source frequency adjustment module, the FP cavity frequency adjustment module, and the external cavity frequency adjustment module are coordinated to modulate the seed beam's intrinsic frequency f1, the FP cavity's resonant frequency f2, and the feedback loop's external cavity's resonant frequency f3 to satisfy the external cavity self-injection locking condition, thereby forming a frequency-locked laser. The external cavity self-injection locking conditions include: The difference between the intrinsic frequency f1 of the seed beam and the resonant frequency f2 of the FP cavity is less than the external cavity self-injection locking range of the external cavity of the feedback loop. The difference between the resonant frequency f2 of the FP cavity and the resonant frequency f3 of the external cavity of the feedback loop is less than or equal to half of the free spectral range of the external cavity of the feedback loop.

2. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The FP cavity frequency adjustment module and the external cavity frequency adjustment module are electrically controlled displacement modules; the electrically controlled displacement modules are respectively mounted on at least one optical component of the external cavity of the feedback loop and the FP cavity; The electrically controlled displacement module is used to change the cavity length of the outer cavity of the feedback loop or the FP cavity, or the electrically controlled displacement module is used to change the optical path of the beam in the optical component to adjust the resonant frequency of the outer cavity of the feedback loop or the FP cavity.

3. The frequency-modulated external cavity laser device according to claim 2, characterized in that, The outer cavity of the feedback loop and the FP cavity each include at least one reflection unit, and the electronically controlled displacement module is mounted on the reflection unit; The electronically controlled displacement module is used to change the cavity length of the feedback loop outer cavity or the FP cavity according to the formula Δf / f=ΔL / L, so as to adjust the resonant frequency of the feedback loop outer cavity or the FP cavity; Where f is the current resonant frequency of the external cavity of the feedback loop or the FP cavity, Δf is the change in the resonant frequency of the external cavity of the feedback loop or the FP cavity, L is the current cavity length of the external cavity of the feedback loop or the FP cavity, and ΔL is the change in the cavity length of the external cavity of the feedback loop or the FP cavity.

4. The frequency-modulated external cavity laser device according to claim 2, characterized in that, The outer cavity of the feedback loop and the FP cavity each include at least one prism unit, and the electronically controlled displacement module is mounted on the prism unit; The electronically controlled displacement module is used to change the optical path of the beam in the optical component according to the formula Δf / f=n1*ΔL / (n2*L) to adjust the resonant frequency of the external cavity of the feedback loop or the FP cavity; Where f is the current resonant frequency of the external cavity of the feedback loop or the FP cavity, Δf is the change in the resonant frequency of the external cavity of the feedback loop or the FP cavity, n2*L is the total optical path of the external cavity of the feedback loop or the FP cavity, and n1*ΔL is the change in the optical path of the external cavity of the feedback loop or the FP cavity.

5. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The FP cavity frequency adjustment module and the external cavity frequency adjustment module are respectively an electrically controlled refractive index module or a thermally controlled refractive index module; the electrically controlled refractive index module or the thermally controlled refractive index module is located in the external cavity of the feedback loop or in the FP cavity; The electrically controlled refractive index module is used to change the refractive index through the electro-optic effect, and the thermally controlled refractive index module is used to change the refractive index through the thermo-optic effect, so as to adjust the optical path of the light beam in the electrically controlled refractive index module or the thermally controlled refractive index module, thereby adjusting the resonant frequency of the external cavity of the feedback loop or the FP cavity.

6. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The seed light source includes a first end and a second end; the seed beam is output from the first end of the seed light source, and the transmitted beam is input from the first end of the seed light source; The outer cavity of the feedback loop also includes a first collimation unit, a unidirectional transmission unit, and a reflection unit; The first collimation unit is used to collimate the seed beam; The unidirectional transmission unit is used to transmit the seed beam to the FP cavity and block the reflected beam from the FP cavity from entering the seed light source; The reflection unit is used to reflect the transmitted light beam from the FP cavity back to the seed light source to form a feedback optical path.

7. The frequency-modulated external cavity laser device according to claim 6, characterized in that, The first collimation unit includes a first lens, the unidirectional transmission unit includes a polarizing beam splitter, a first quarter-wave plate, a second quarter-wave plate and a second lens in sequence, and the reflection unit includes a first reflecting mirror; The FP cavity is located between the first quarter-wave plate and the second quarter-wave plate; The second lens is located between the FP cavity and the second quarter-wave plate or between the second quarter-wave plate and the first reflector.

8. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The seed light source includes a first end and a second end; the seed beam is output from the first end of the seed light source, and the transmitted beam is input from the first end of the seed light source; or, the seed beam is output from the first end of the seed light source, and the transmitted beam is input from the second end of the seed light source. The outer cavity of the feedback loop also includes a unidirectional transmission unit and a light beam steering unit; The unidirectional transmission unit is used to transmit the seed beam to the FP cavity and block the reflected beam from the FP cavity from entering the seed light source; The light steering unit is used to change the transmission direction of the transmitted light beam in the FP cavity so that the transmitted light beam is fed back to the seed light source to form a feedback light path.

9. The frequency-modulated external cavity laser device according to claim 8, characterized in that, The unidirectional transmission unit includes a circulator, and the light deflection unit includes a second reflector, a third reflector, and a fourth reflector; The beam transmission path within the frequency-modulated external cavity laser device is as follows: The seed beam is output from the first end of the seed light source, input from the first end of the circulator, output from the second end of the circulator, and incident on the FP cavity to be transmitted, forming the transmitted beam; the transmitted beam is reflected sequentially by the second reflector, the third reflector and the fourth reflector and then incident on the third end of the circulator, and output from the first end of the circulator to the seed light source.

10. The frequency-modulated external cavity laser device according to claim 8, characterized in that, The unidirectional transmission unit includes an isolator, and the light deflection unit includes a fifth mirror, a sixth mirror, a seventh mirror, and an eighth mirror; The beam transmission path within the frequency-modulated external cavity laser device is as follows: The seed beam is output from the first end of the seed light source, input from the first end of the isolator, and output from the second end of the isolator. It is incident on the FP cavity and transmitted to form the transmitted beam. The transmitted beam is reflected sequentially by the fifth mirror, the sixth mirror, the seventh mirror and the eighth mirror before being incident on the second end of the seed light source.

11. The frequency-modulated external cavity laser device according to any one of claims 6-10, characterized in that, The unidirectional transmission unit further includes at least one isolator, and at least one of the isolators is located between the seed light source and the FP cavity.

12. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The FP cavity includes a ninth mirror and a tenth mirror that are parallel to each other. The seed beam is incident through the ninth mirror and exits through the tenth mirror. Alternatively, the FP cavity includes an eleventh mirror, a twelfth mirror, and a thirteenth mirror. The seed beam is incident on the eleventh mirror, reflected sequentially by the twelfth and thirteenth mirrors, and then exits from the eleventh mirror.

13. The frequency-modulated external cavity laser device according to claim 1, characterized in that, The seed light source includes a semiconductor laser; or, the seed light source includes a combination of a gain chip and a filter, wherein the filter is located at any position in the outer cavity of the feedback loop.

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