Fourier domain mode locked laser based on dynamic laser setup process and control method

Abstract

The application discloses a Fourier domain mode locked laser based on a laser dynamic establishment process and a control method, and comprises a ring laser cavity which is composed of an optical amplifier, a first isolator, a second isolator, an adjustable filter, a delay optical fiber, a coupler and a polarization controller or an optical amplifier, a first isolator, a second isolator, an adjustable filter, a delay optical fiber, a coupler, an intensity modulator and a polarization controller. When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the adjustable filter, the optical amplifier or the intensity modulator is controlled to restart, so that the laser signal is restarted instead of the signal in the continuous gain cavity, the residual dispersion in the cavity is resisted, high coherent swept laser output is realized, any dispersion compensation technology is not needed, the scheme is simple, the requirements of the devices used for the laser are low, environment control technology is not needed, the scheme has strong robustness, the cost is reduced, and the Fourier domain mode locked laser can be applied to any waveband.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more particularly to a Fourier domain mode-locked laser and its control method based on the dynamic laser setup process. Background Technology

[0002] Fourier-domain mode-locked lasers (SLDs) are among the achievable high-speed frequency-sweeping light sources. They can be applied to optical coherence tomography and are widely used in fields such as optical radar, optical sensing, ultrafast pulse generation, and optical device performance characterization. A SLD uses a long optical fiber as a delay line within the laser cavity, ensuring that each wavelength circulates once within the cavity and reaches the sweep filter at the exact wavelength it was tuned to. Therefore, each wavelength does not need to be reconstructed from noise, and the sweep speed is not limited by the laser oscillation settling time but is equal to the filter's tuning speed, thus achieving a high sweep speed. However, due to the combined effects of the resonant cavity dispersion and nonlinearity of the SLD, as well as the noise of the optical amplifier, frequency shifts caused by linewidth gain factors, filter linewidth, and modulation frequency detuning, incoherent components are generated, causing the signal to quickly become unstable. Furthermore, there is no strong correlation between the various frequency components, resulting in poor coherence and stability.

[0003] To address this, existing solutions typically employ dispersion compensation (dispersion-compensating fiber, dispersion-shifting fiber, chirped grating), temperature stabilization control, and feedback compensation to improve the coherence of Fourier-domain mode-locked lasers. However, these solutions require expensive custom-designed components, which not only increases the complexity and cost of the laser but also makes the components susceptible to environmental influences, making it difficult to guarantee the long-term stability of the laser. Furthermore, the coherence length of the laser remains relatively low.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a Fourier domain mode-locked laser and control method based on the laser dynamic establishment process, so as to solve the problems of high complexity, high cost, susceptibility to environmental influence and low coherence of existing Fourier domain mode-locked laser technologies for improving coherence.

[0006] The technical solution of the present invention is as follows:

[0007] A Fourier domain mode-locked laser based on a laser dynamic setup process includes an optical amplifier for providing gain to the laser signal and modulating the intensity of the laser signal.

[0008] First and second isolators are used to enable unidirectional operation of laser signals;

[0009] An adjustable filter for sweeping signal frequency control of a laser signal;

[0010] A delay fiber for providing a buffer for a laser signal;

[0011] A coupler for outputting a laser signal and maintaining the laser signal in a cavity;

[0012] A polarization controller for regulating a polarization state of a ring laser cavity;

[0013] The optical amplifier, the first isolator, the second isolator, the adjustable filter, the delay fiber, the coupler and the polarization controller constitute a ring laser cavity;

[0014] An arbitrary waveform generator is connected to the optical amplifier and the adjustable filter respectively, the arbitrary waveform generator is used for outputting a first control signal to drive the optical amplifier, outputting a second control signal to drive the adjustable filter, and is used for controlling the optical amplifier to restart when a dispersion amount in the ring laser cavity exceeds a bandwidth range of the adjustable filter.

[0015] Further provided by the application, the Fourier domain mode locked laser further comprises: a comb filter; the comb filter is arranged in the laser cavity, and the comb filter is used for frequency domain discretization of a laser signal.

[0016] Further provided by the application, the optical amplifier is multiple, and the multiple optical amplifiers are in series or parallel.

[0017] Further provided by the application, the Fourier domain mode locked laser further comprises: an optical circulator and a reflector; the optical circulator is connected to the delay fiber, and the reflector is connected to the delay fiber.

[0018] Further provided by the application, the optical amplifier is one or more of a semiconductor optical amplifier, a doped fiber amplifier, a Raman amplifier and a parametric amplifier; the coupler is an optical fiber coupler or a free space optical coupler; the delay fiber is one or more of any kind of single mode fiber or multimode fiber; and the polarization controller is one or more of an optical fiber online polarization controller or a free space polarization controller.

[0019] A control method based on the Fourier domain mode locked laser based on the above-mentioned laser dynamic establishment process, comprising:

[0020] The arbitrary waveform generator is controlled to output a first control signal to drive the optical amplifier and output a second control signal to drive the adjustable filter;

[0021] The optical amplifier is controlled to restart when a dispersion amount in the ring laser cavity exceeds a bandwidth range of the adjustable filter.

[0022] A Fourier domain mode locked laser based on a dynamic laser setup process, comprising:

[0023] An optical amplifier for providing gain to a laser signal;

[0024] A first isolator and a second isolator for unidirectional running of the laser signal;

[0025] An adjustable filter for frequency control of the laser signal;

[0026] An intensity modulator for intensity modulation of the laser signal;

[0027] A delay fiber for providing a buffer to the laser signal;

[0028] A coupler for outputting the laser signal and maintaining the laser signal in a cavity;

[0029] A polarization controller for regulating a polarization state of the ring laser cavity;

[0030] The optical amplifier, the first isolator, the second isolator, the adjustable filter, the intensity modulator, the delay fiber, the coupler and the polarization controller constitute a ring laser cavity;

[0031] An arbitrary waveform generator is connected to the intensity modulator and the adjustable filter, respectively, and the arbitrary waveform generator is used to output a first control signal to drive the intensity modulator, output a second control signal to drive the adjustable filter, and control the intensity modulator to restart when a dispersion amount in the ring laser cavity exceeds a bandwidth range of the adjustable filter.

[0032] Further provided in the present application, the Fourier domain mode locked laser further comprises a comb filter, and the comb filter is used to discretize the laser signal in the frequency domain.

[0033] A control method based on the Fourier domain mode locked laser based on a dynamic laser setup process described above, comprising:

[0034] Controlling an arbitrary waveform generator to output a first control signal to drive an intensity modulator and output a second control signal to drive an adjustable filter;

[0035] Controlling the intensity modulator to restart when a dispersion amount in the ring laser cavity exceeds a bandwidth range of the adjustable filter.

[0036] Further provided in the present application, the step of controlling the arbitrary waveform generator to output the first control signal to drive the optical amplifier comprises:

[0037] pulse signal modulate the first control signal to time domain discrete the laser signal.

[0038] The Fourier domain mode-locked laser based on a dynamic establishment process and the control method have the following beneficial effects:

[0039] The application controls the optical amplifier or the intensity modulator to restart when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the adjustable filter, thereby replacing the continuous gain cavity signal by restarting the laser signal to resist the residual dispersion in the cavity, and then realizing high-coherent sweep laser output. Compared with the conventional Fourier mode-locked laser, the application does not need any dispersion compensation technology, has a simple scheme, has lower requirements for the devices used by the laser, does not need environmental control technology assistance, has strong robustness, reduces the cost, and can be applied to Fourier domain mode-locked lasers of any waveband. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to the structures shown in the drawings without creative labor.

[0041] Figure 1 is a process diagram of the Fourier domain mode-locked laser signal generating incoherent components.

[0042] Figure 2 is the principle of the Fourier domain mode-locked laser in an embodiment of the present application Figure 1 .

[0043] Figure 3 is the principle of the Fourier domain mode-locked laser in an embodiment of the present application Figure 2 .

[0044] Figure 4 is the principle of the Fourier domain mode-locked laser in an embodiment of the present application Figure 3 .

[0045] Figure 5 is the flowchart of the control method of the Fourier domain mode-locked laser in an embodiment of the present application.

[0046] Figure 6 is the principle of the Fourier domain mode-locked laser in another embodiment of the present application Figure 1 .

[0047] Figure 7 is the principle of the Fourier domain mode-locked laser in another embodiment of the present application Figure 2 .

[0048] Figure 8 is a flow chart of a control method of a Fourier domain mode locked laser in another embodiment of the present application.

[0049] In the drawings: 1, optical amplifier; 2, first isolator; 3, second isolator; 4, tunable filter; 5, delay fiber; 6, coupler; 7, polarization controller; 8, arbitrary waveform generator; 9, comb filter; 10, intensity modulator; 11, optical circulator; 12, reflector. DETAILED DESCRIPTION

[0050] The present application provides a Fourier domain mode locked laser based on a dynamic establishment process of a laser and a control method. In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0051] In the embodiments and the patent application scope, unless the article has a special definition in the text, "one", "a", "said" and "the" can also include the plural form. If the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features.

[0052] It should be further understood that the phrase "comprising" used in the specification of the present application means that the features, integers, steps, operations, elements and / or components exist, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their combinations. It should be understood that when an element is said to be "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be an intermediate element. In addition, "connection" or "coupling" used herein can include wireless connection or wireless coupling. The phrase "and / or" used herein includes all or any unit and all combinations of the associated listed items.

[0053] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as that generally understood by those skilled in the art in the field to which the present application belongs. It should also be understood that terms such as those defined in a general dictionary should be understood as having meanings consistent with those in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as such.

[0054] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0055] A laser has a laser cavity, also known as a resonant cavity. The function of the resonant cavity is to preferentially amplify light of a specific frequency and consistent direction, while suppressing light of other frequencies and directions. Photons that do not meet the resonant frequency or move along the axis of the resonant cavity cannot be amplified. Photons that meet the resonant frequency and move along the axis will continue to propagate within the cavity, oscillating repeatedly as they travel back and forth within the ring cavity. During this process, they continuously encounter stimulated particles, producing stimulated emission. The photons will continuously multiply, forming a strong beam of light within the cavity with a consistent propagation direction and a stable relationship between frequency and phase—this is a laser.

[0056] Fourier-domain mode-locked lasers are devices used to obtain high-speed frequency-sweeping light sources. Fourier-domain mode-locked lasers generally have two architectures: spatial structures based on bulk optical elements and fiber architectures based on fiber optic devices. Mode-locked fiber lasers can be further classified into linear cavities and ring cavities based on their cavity structure. A ring cavity refers to a cavity structure formed by interconnected optical components.

[0057] The inventors discovered that after a Fourier-domain mode-locked laser signal travels dozens of times within a ring resonant cavity, a highly coherent swept-frequency laser signal can be established from amplified spontaneous emission, such as... Figure 1 As shown in Figure a, where, Figure 1 The horizontal axis represents the number of round trips within the ring laser cavity, and the vertical axis represents the sampling point index. After passing through the interferometer, the swept laser can form stable interference fringes in the time domain, such as... Figure 1 As shown in Figure b. However, as the number of round trips of the laser signal within the cavity increases, as... Figure 1 As shown in Figure c, incoherent components will be generated in the laser signal, significantly degrading the laser's coherence. The generation rate of these incoherent components is mainly affected by the total dispersion of the laser cavity, the sweep rate, and the gain factor of the optical amplifier linewidth. This process will repeat until the laser trace is filled with incoherent components, degrading the laser coherence length and signal-to-noise ratio. Existing solutions typically employ dispersion compensation, temperature stabilization control, and feedback compensation to improve the coherence of Fourier-domain mode-locked lasers. However, these solutions require expensive custom-designed components, increasing the complexity and cost of the laser. Furthermore, these components are susceptible to environmental influences, making it difficult to guarantee the long-term stability of the laser, while the coherence length remains relatively low.

[0058] In order to solve the above technical problems, the application provides a Fourier domain mode-locked laser based on a dynamic establishment process of laser and a control method, wherein when the dispersion in the ring laser cavity exceeds the bandwidth range of the tunable filter, the optical amplifier or the intensity modulator is restarted, so that the laser signal is restarted to replace the continuous gain cavity signal, the residual dispersion in the cavity is resisted, and high-coherent swept laser output is realized. Compared with the conventional Fourier mode-locked laser, the application does not need any dispersion compensation technology, the scheme is simple, the requirements for the devices used by the laser are low, the environmental control technology is not needed, the robustness is high, the cost is reduced, and the Fourier domain mode-locked laser of any waveband can be applied.

[0059] Please refer to Figure 2 and Figure 3 , the application provides a preferred embodiment of the Fourier domain mode-locked laser based on the dynamic establishment process of laser.

[0060] In some embodiments, as Figure 1 shown, the Fourier domain mode-locked laser based on the dynamic establishment process of laser provided by the application comprises an optical amplifier 1, a first isolator 2, a second isolator 3, a tunable filter 4, a delay optical fiber 5, a coupler 6, a polarization controller 7 and an arbitrary waveform generator 8. The optical amplifier 1, the first isolator 2, the second isolator 3, the tunable filter 4, the delay optical fiber 5, the coupler 6 and the polarization controller 7 constitute a ring laser cavity. The optical amplifier 1 is used to provide gain for the laser signal and modulate the intensity of the laser signal. The first isolator 2 and the second isolator 3 are used to make the laser signal run in one direction. The tunable filter 4 is used to control the frequency of the swept output signal of the laser signal. The delay optical fiber 5 is used to provide a buffer for the laser signal. The coupler 6 is used to output the laser signal and maintain the laser signal in the cavity. The polarization controller 7 is used to regulate the polarization state of the ring laser cavity. The arbitrary waveform generator 8 is connected with the optical amplifier 1 and the tunable filter 4, respectively. The arbitrary waveform generator 8 is used to output a first control signal to drive the optical amplifier 1, output a second control signal to drive the tunable filter 4, and restart the optical amplifier 1 when the dispersion in the ring laser cavity exceeds the bandwidth range of the tunable filter 4. In this embodiment, the mode-locked laser is composed of the ring laser cavity composed of the arbitrary waveform generator 8 and the optical amplifier 1, the first isolator 2, the second isolator 3, the tunable filter 4, the delay optical fiber 5, the coupler 6 and the polarization controller 7.

[0061] The arbitrary waveform generator 8 can generate a first control signal and a second control signal, wherein the second control signal is a driving electrical signal of the tunable filter 4, for example, a sinusoidal signal can be used to drive the tunable filter 4 to dynamically filter the laser signal. The arbitrary waveform generator 8 can trigger the driving and management of the tunable filter 4 and the optical amplifier 1 at the same time, so that the arbitrary waveform generator 8 can periodically form wavelength scanning and gain switching in the ring laser cavity. The arbitrary waveform generator 8 can calculate the switching period of the optical amplifier 1 according to the bandwidth tolerance range of the tunable filter 4 and the dispersion accumulation speed, so that the laser signal cannot accumulate a large amount of dispersion during the establishment process. The filtering principle of the tunable filter 4 is that the frequency v of the sinusoidal signal is selected according to the length L of the delay optical fiber 5, v = c / 2nL, wherein n is the refractive index of the optical fiber, and c represents the speed of light. This selection can ensure that each wavelength reaches the tunable filter 4 again after circulating in the cavity for one cycle, and the tunable filter 4 is tuned to this wavelength at this time to make it pass, so as to meet the dynamic filtering, wherein the amplitude voltage and the bias voltage of the sinusoidal signal are selected according to the requirement of the sweep frequency range of the tunable filter 4. The first control signal is the switching signal of the optical amplifier 1, and the first control signal can be a periodic square wave signal. The periodic square wave signal can drive the optical amplifier 1 to control the optical amplifier 1 to be closed or re-opened. In this way, the first control signal output by the arbitrary waveform generator 8 can realize the restart of the optical amplifier 1, and further realize the restart of the laser.

[0062] The first isolator 2 and the second isolator 3 can realize one-way operation of the laser signal and protect the optical amplifier 1 from reflected light and backscattered light, while adding an isolator to the ring laser can avoid optical resonance effect, ensure the flatness of the swept spectrum, and it should be noted that the optical resonance effect requires a light path that can be passed in both forward and reverse directions, and assuming its length is L, in the case of resonance effect, the laser component whose frequency satisfies c / 2nL will be filtered out or enhanced, which will cause the swept laser spectrum to be uneven and deteriorate the laser performance. The isolator can block the reverse passing light path and avoid resonance effect. The delay fiber 5 can provide a buffer for the laser signal in the ring laser cavity. The coupler 6 is used to realize the output of the laser signal and maintain the effective oscillation of the laser signal. The polarization controller 7 can realize the regulation of the polarization state of the laser in the cavity, so that the laser signal can be effectively amplified in the optical amplifier 1; the adjustable filter 4 can be a mechanical or integrated adjustable filter 4 based on a scanning lens and a grating, controlled by a piezoelectric ceramic, and narrow-band filtered by a signal generated by an arbitrary waveform generator 8. It should be noted that the connection order of the optical amplifier 1, the first isolator 2, the second isolator 3, the adjustable filter 4, the delay fiber 5, the coupler 6 and the polarization controller 7 can be adjusted, Figure 2 The connection order of the optical amplifier 1, the first isolator 2, the second isolator 3, the adjustable filter 4, the delay fiber 5, the coupler 6 and the polarization controller 7 can be adjusted,

[0063] In specific implementation, the adjustable filter 4 can scan the laser frequency components in the ring laser cavity, and the frequency of the second control signal corresponds to the cavity fundamental frequency or its multiple. The optical amplifier 1 serves as a gain medium for the laser signal in the ring laser cavity, and cooperates with the delay fiber 5, the coupler 6, the polarization controller 7, the first isolator 2 and the second isolator 3 to form a Fourier domain mode locking mechanism. When the dispersion in the ring laser cavity exceeds the bandwidth range of the adjustable filter 4, the arbitrary waveform generator 8 controls the optical amplifier 1 to restart, thereby restarting the laser operation before the incoherent components are generated, to resist the generation of incoherent components caused by residual dispersion and nonlinearity in the ring laser cavity through laser signal restart, and improve the coherence and signal-to-noise ratio of the Fourier domain mode locking laser.

[0064] Compared with a conventional Fourier mode-locked laser, the application can weaken the influence of residual dispersion in the laser cavity without any dispersion compensation technology, greatly reduce the influence of dispersion on the stable operation of the laser cavity, better improve the coherence of the Fourier mode-locked laser, overcome the coherence limitation of the Fourier mode-locked laser, and reduce the cost. Compared with the existing dispersion compensation scheme of the Fourier mode-locked laser, the scheme is applicable to Fourier mode-locked lasers in any waveband, and is especially suitable for special wavebands such as one micron and other wavebands where dispersion compensation is difficult to implement.

[0065] In some examples, the optical amplifier 1 is an implementer of gain and laser restart of the laser signal in the ring laser cavity, and can be but is not limited to a semiconductor optical amplifier, a doped fiber amplifier, a Raman amplifier, and a parametric amplifier. The optical amplifier 1 can be formed in different wavebands by selecting different types of semiconductor materials, doped fibers, and pump light, and can be set to one or more according to the loss of the laser cavity, and the multiple optical amplifiers 1 are in series or parallel, for example, the series connection is required when high laser cavity loss is required, and the parallel connection is required when high bandwidth is required.

[0066] In some examples, the coupler 6 can split the laser signal in different proportions, can realize the laser output in the ring laser cavity and maintain the effective oscillation of the laser signal in the ring laser cavity, and can be a fiber coupler 6 or a free-space optical coupler 6 based on a fiber fusion taper, a waveguide beam splitter, or the like.

[0067] In some examples, the delay fiber 5 can provide a buffer for the laser signal in the ring laser cavity to avoid the re-establishment of the laser signal from the amplified spontaneous emission and improve the sweep speed. In one implementation, the delay fiber 5 can be one or more of any kind of single-mode fiber or multi-mode fiber, that is, the delay fiber 5 can also be composed of any kind of single-mode fiber and multi-mode fiber, and can realize single one-way propagation.

[0068] Further, as Figure 4 shown, the Fourier domain mode-locked laser further includes an optical circulator 11 and a reflector 12; the optical circulator 11 is connected with the delay fiber 5, and the reflector 12 is connected with the delay fiber 5.

[0069] Specifically, when bidirectional propagation delay is required, the delay fiber 5 can be combined with an optical circulator to achieve bidirectional propagation delay in cooperation with the reflector. In some embodiments, the reflector can be a total reflection fiber ring, a mirror, a Faraday rotatory mirror, or the like.

[0070] In some embodiments, the polarization controller 7 can regulate the polarization state of the laser signal in the ring laser cavity, so that the laser signal can work in the optimal state in the optical amplifier 1, so that the laser signal can be effectively amplified. The polarization controller 7 can be, but is not limited to, an on-line polarization controller 7 based on different types of three-ring, double-ring, extrusion, etc. or a free-space polarization controller 7 composed of multiple glass plates.

[0071] In some embodiments, as shown in Figure 3 The Fourier domain mode-locked laser further comprises a comb filter 9, wherein the comb filter 9 is arranged in the laser cavity, and the comb filter 9 is used for frequency domain discretization of the laser signal.

[0072] In this embodiment, by adding a comb filter 9 in the ring laser cavity, the comb filter 9 can perform frequency domain discretization on the laser signal in the ring laser cavity, and the comb filter 9 can be used to pass the signal with wavelength at the transmission peak of the tunable filter 4 by using the narrower instantaneous linewidth of the comb filter 9 relative to the tunable filter 4, so as to optimize the correlation of the laser signal. In this embodiment, the comb filter 9 can be a comb spectral filter based on different principles such as Fabry-Perot interferometer, Mach-Zehnder interferometer, fiber ring, optical waveguide ring, etc.

[0073] In some embodiments, as shown in Figure 5 The present application provides a control method of the Fourier domain mode-locked laser based on the above-mentioned laser dynamic establishment process, which comprises the following steps:

[0074] S100, controlling an arbitrary waveform generator to output a first control signal to drive an optical amplifier and output a second control signal to drive a tunable filter;

[0075] S200, when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, controlling the optical amplifier to restart.

[0076] In this embodiment, the arbitrary waveform generator can simultaneously trigger, drive, and manage the tunable filter and the optical amplifier, enabling the arbitrary waveform generator to periodically perform wavelength scanning and gain switching within the ring laser cavity. The arbitrary waveform generator can calculate the switching period of the optical amplifier based on the bandwidth tolerance range of the tunable filter and the dispersion accumulation rate, preventing the accumulation of large amounts of dispersion during laser signal establishment. When the dispersion within the ring laser cavity exceeds the bandwidth range of the tunable filter, the arbitrary waveform generator controls the optical amplifier to restart, thereby restarting laser operation before the generation of incoherent components. This restarting of the laser signal counteracts the generation of incoherent components caused by residual dispersion and nonlinearity within the ring laser cavity, improving the coherence and signal-to-noise ratio of the Fourier domain mode-locked laser.

[0077] In some embodiments, such as Figure 6 As shown, the present invention also provides another embodiment of a Fourier domain mode-locked laser, which includes: an optical amplifier 1, a first isolator 2, a second isolator 3, a tunable filter 4, an intensity modulator 10, a delay fiber 5, a coupler 6, a polarization controller 7, and an arbitrary waveform generator 8. The optical amplifier 1, the first isolator 2, the second isolator 3, the tunable filter 4, the intensity modulator 10, the delay fiber 5, the coupler 6, and the polarization controller 7 constitute a ring laser cavity. The optical amplifier 1 provides gain for the laser signal; the first isolator 2 and the second isolator 3 enable unidirectional operation of the laser signal; the tunable filter 4 controls the frequency of the laser signal by sweeping the signal; the intensity modulator 10 modulates the intensity of the laser signal; the delay fiber 5 provides buffering for the laser signal; the coupler 6 outputs the laser signal and maintains the laser signal oscillation within the cavity; the polarization controller 7 regulates the polarization state of the ring laser cavity; and the arbitrary waveform generator 8 is connected to the intensity modulator 10 and the tunable filter 4, respectively. The arbitrary waveform generator 8 outputs a first control signal to drive the intensity modulator 10, outputs a second control signal to drive the tunable filter 4, and controls the intensity modulator 10 to restart when the dispersion within the ring laser cavity exceeds the bandwidth of the tunable filter 4.

[0078] In the embodiment, the arbitrary waveform generator 8 is used to trigger and manage the tunable filter 4 and the intensity modulator 10 simultaneously, so as to periodically form wavelength scanning and gain switching in the cavity. The tunable filter 4 can realize scanning of the laser frequency component in the cavity, wherein the scanning drive signal frequency corresponds to the cavity fundamental frequency or its multiple. The intensity modulator 10 as an implementer of laser restart can realize laser restart and time domain discretization, and realize intensity modulation of the laser signal. The optical amplifier 1 is a gain device of the laser signal in the ring cavity. The first isolator 2 and the second isolator 3 are used to realize unidirectional operation of the laser and to protect the optical amplifier 1 from reflected light and backscattered light. The delay fiber 5 is used to provide a buffer for the cavity scanning laser signal, to avoid re-establishment of the laser signal from amplified spontaneous emission, and to improve the scanning speed. The coupler 6 is used to realize the cavity laser output and maintain effective oscillation of the laser in the cavity. The polarization controller 7 is used to realize regulation of the polarization state of the laser in the cavity, so that the laser signal can be effectively amplified in the optical amplifier 1, and the laser signal can pass through the intensity modulator 10 with low loss and high extinction ratio.

[0079] The light intensity modulator 10 is used to realize intensity modulation of the optical signal, and can be an electro-optic modulator, an acousto-optic modulator, a magneto-optic modulator, a semiconductor electro-absorption modulator, a micro-mechanical optical switch, or a direct modulation of a pump electrical signal or an optical signal of the optical amplifier 1. The tunable filter 4 can be a tunable filter 4 based on a scanning lens cooperating with a grating, a piezoelectric ceramic controlled mechanical or integrated tunable filter 4, a signal control generated by an arbitrary waveform generator 8, and narrowband filtering of the optical signal. The polarization controller 7 can be, but is not limited to, an on-line polarization controller 7 based on different types of optical fibers such as a three-ring type, a double-ring type, and an extrusion type, or a free-space polarization controller 7 composed of multiple glass sheets. The optical amplifier 1 can be, but is not limited to, a semiconductor optical amplifier 1, a doped optical fiber amplifier, a Raman amplifier, and a parametric amplifier. The optical amplifier 1 can be formed in different wavelength bands by selecting different types of semiconductor materials, doped optical fibers, and pump light, and can be set to one or more according to the loss of the laser cavity, and the multiple optical amplifiers 1 are connected in series or in parallel. For example, when high laser loss is required, the series connection mode is used, and when high bandwidth is required, the parallel connection mode is used. The coupler 6 can be an optical fiber coupler 6 based on a fiber taper, a waveguide beam splitter, or a free-space optical coupler 6. In an implementation manner, the delay optical fiber 5 can be one or more of any kind of single-mode optical fiber or multi-mode optical fiber, that is, the delay optical fiber 5 can also be composed of any kind of single-mode optical fiber and multi-mode optical fiber, and can realize single-time one-way propagation. When bidirectional propagation delay is required, the delay optical fiber 5 can be combined with an optical circulator and the reflector to realize bidirectional propagation delay. In some embodiments, the reflector can be a full-reflection optical fiber ring, a mirror, a Faraday optical rotator, and the like.

[0080] In specific implementation, the arbitrary waveform generator 8 simultaneously triggers the driving of the tunable filter 4 and the intensity modulator 10, selects the switching period of the intensity modulator 10 according to the filter bandwidth tolerance range and the dispersion accumulation speed, so that the laser cannot accumulate a large amount of dispersion in the establishment process. When the dispersion amount exceeds the filter bandwidth range, the high-coherence Fourier-domain mode-locked laser signal is re-established by switching the intensity modulator 10, so as to prevent the generation of incoherent components caused by dispersion and nonlinearity in the ring laser cavity, and improve the coherence and signal-to-noise ratio of the Fourier-domain mode-locked laser. Compared with the conventional Fourier-mode-locked laser, any dispersion compensation technology is not required, the scheme is simple, the requirements for the devices used by the laser are low, environmental control technology is not required, the robustness is high, the cost is reduced, and the Fourier-domain mode-locked laser can be applied to any wavelength band.

[0081] In some embodiments, as Figure 7As shown, the Fourier-domain mode-locked laser further comprises a comb filter 9; the comb filter 9 is used for frequency-domain discretization of the laser signal.

[0082] In the embodiment, by adding a comb filter 9 in the ring laser cavity, the comb filter 9 can perform frequency-domain discretization on the laser signal in the ring laser cavity, and the comb filter 9 can be used to pass the signal with the wavelength at the transmission peak of the tunable filter 4 by using the narrower instantaneous linewidth of the comb filter 9 relative to the tunable filter 4, so as to optimize the coherence of the laser signal. In the embodiment, the comb filter 9 can be a comb spectral filter based on different principles such as Fabry-Perot interferometer, Mach-Zehnder interferometer, fiber ring, optical waveguide ring, etc. It should be noted that if the intensity modulator 10 is used to perform time-domain discretization on the laser signal, the pulse frequency of the intensity modulator 10 driven by the arbitrary waveform generator should be synchronized with the frequency at which the comb filter performs time-domain discretization on the laser signal.

[0083] In some embodiments, as shown, Figure 8 The application provides a control method of the Fourier-domain mode-locked laser based on the above-mentioned laser dynamic establishment process, which comprises the following steps:

[0084] S100, controlling the arbitrary waveform generator to output a first control signal to drive the intensity modulator and output a second control signal to drive the tunable filter;

[0085] S200, when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, controlling the intensity modulator to restart.

[0086] In the embodiment, the arbitrary waveform generator can simultaneously trigger the driving and management of the tunable filter and the intensity modulator, so that the arbitrary waveform generator can periodically form wavelength scanning and gain switching in the ring laser cavity. The arbitrary waveform generator can calculate the switching period of the intensity modulator according to the bandwidth tolerance range of the tunable filter and the dispersion accumulation speed, so that the laser signal cannot accumulate a large amount of dispersion during the establishment process. When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, the arbitrary waveform generator controls the intensity modulator to restart, so as to restart the laser operation before the non-coherent component is generated, to resist the generation of the non-coherent component caused by the residual dispersion and nonlinearity in the ring laser cavity through the laser signal restart, and to improve the coherence and signal-to-noise ratio of the Fourier-domain mode-locked laser.

[0087] In some embodiments, the step of controlling the arbitrary waveform generator to output a first control signal to drive the optical amplifier comprises the following steps:

[0088] S110, pulse signal modulation is performed on the first control signal to discretize the laser signal in time domain.

[0089] In the embodiment, the first control signal loaded on the intensity modulator is pulse signal, which can discretize the laser signal in time domain, synchronize the pulse frequency with the frequency of the comb filter, and improve the signal-to-noise ratio of the laser signal.

[0090] In summary, the application provides a Fourier domain mode-locked laser based on a dynamic establishment process and a control method, which is based on the dynamic establishment process of the Fourier domain mode-locked laser, opens the intensity modulator or the optical amplifier before the non-coherent component of the laser is generated, and restarts the operation of the laser to improve the coherence and the signal-to-noise ratio of the Fourier domain mode-locked laser. The application mainly solves the problem of large residual dispersion of the Fourier domain mode-locked laser cavity and poor laser coherence, and does not need to introduce a customized device or use a strict constant temperature vibration isolation system. The scheme is simple and has low cost.

[0091] It should be understood that the application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the application.

Claims

1. A Fourier domain mode-locked laser based on a dynamic laser setup process, characterized in that, include: An optical amplifier used to provide gain for laser signals and modulate the intensity of laser signals; First and second isolators are used to enable unidirectional operation of laser signals; An adjustable filter used for sweep frequency control of laser signals; Delay fiber used to buffer laser signals; Couplers used for outputting laser signals and maintaining the oscillation of laser signals within the cavity; A polarization controller used to regulate the polarization state of a ring laser cavity; The optical amplifier, the first isolator, the second isolator, the tunable filter, the delay fiber, the coupler, and the polarization controller constitute a ring laser cavity; An arbitrary waveform generator is connected to the optical amplifier and the tunable filter respectively. The arbitrary waveform generator is used to output a first control signal to drive the optical amplifier, output a second control signal to drive the tunable filter, and control the optical amplifier to restart when the dispersion in the ring laser cavity exceeds the bandwidth range of the tunable filter.

2. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 1, characterized in that, Also includes: A comb filter; the comb filter is disposed in the laser cavity and is used to perform frequency domain discretization on the laser signal.

3. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 1, characterized in that, The optical amplifier is multiple, and the multiple optical amplifiers are connected in series or in parallel.

4. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 1, characterized in that, Also includes: Optical circulators and reflectors; The optical circulator is connected to the time-delay fiber, and the reflector is connected to the time-delay fiber.

5. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 1, characterized in that, The optical amplifier is one or more of a semiconductor optical amplifier, a doped fiber amplifier, a Raman amplifier, and a parametric amplifier; the coupler is a fiber optic coupler or a free-space optical coupler; the delay fiber is one or more of any type of single-mode fiber or multimode fiber; and the polarization controller is one or more of an optical fiber online polarization controller or a free-space polarization controller.

6. A control method for a Fourier domain mode-locked laser based on the laser dynamic setup process as described in any one of claims 1-5, characterized in that, include: The arbitrary waveform generator outputs a first control signal to drive the optical amplifier and a second control signal to drive the adjustable filter. The optical amplifier is restarted when the dispersion within the ring laser cavity exceeds the bandwidth of the tunable filter.

7. A Fourier domain mode-locked laser based on a dynamic laser setup process, characterized in that, include: An optical amplifier used to provide gain for laser signals; First and second isolators are used to enable unidirectional operation of laser signals; An adjustable filter used for sweep frequency control of laser signals; An intensity modulator used for modulating the intensity of laser signals; Delay fiber used to buffer laser signals; Couplers used for outputting laser signals and maintaining the oscillation of laser signals within the cavity; A polarization controller used to regulate the polarization state of a ring laser cavity; The optical amplifier, the first isolator, the second isolator, the tunable filter, the intensity modulator, the delay fiber, the coupler, and the polarization controller constitute a ring laser cavity; An arbitrary waveform generator is connected to the intensity modulator and the tunable filter respectively. The arbitrary waveform generator is used to output a first control signal to drive the intensity modulator, output a second control signal to drive the tunable filter, and control the intensity modulator to restart when the dispersion in the ring laser cavity exceeds the bandwidth range of the tunable filter.

8. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 7, characterized in that, Also includes: A comb filter; the comb filter is used to perform frequency domain discretization on the laser signal.

9. A control method for a Fourier domain mode-locked laser based on the laser dynamic setup process as described in claim 7 or 8, characterized in that, include: The arbitrary waveform generator outputs a first control signal to drive the intensity modulator, and outputs a second control signal to drive the adjustable filter. The intensity modulator is restarted when the dispersion within the ring laser cavity exceeds the bandwidth of the tunable filter.

10. The control method according to claim 9, characterized in that, The step of controlling the arbitrary waveform generator to output a first control signal to drive the intensity modulator includes: The first control signal is pulse-modulated to discretize the laser signal in the time domain.

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