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

Abstract

The invention discloses a Fourier domain mode-locked laser based on a laser dynamic establishment process and a control method. An optical amplifier, a first isolator, a second isolator, an adjustable filter, a delay optical fiber, a coupler and a polarization controller or the optical amplifier, the first isolator, the second isolator, the adjustable filter, the delay optical fiber, the coupler, an intensity modulator and the polarization controller form an annular laser cavity. An optical amplifier or an intensity modulator is controlled to be restarted when the dispersion amount in an annular laser cavity exceeds the bandwidth range of an adjustable filter, so that the mode of restarting a laser signal replaces the mode of continuously gaining signals in the cavity, residual dispersion in the cavity is resisted, high-coherence sweep-frequency laser output is further achieved, no dispersion compensation technology is needed, and the cost is reduced. The scheme is simple, the requirement for devices used by the laser is low, no environment control technology assistance is needed, high robustness is achieved, cost is reduced, and the method can be suitable for the Fourier domain mode-locked laser of any wave band.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and in particular to a Fourier domain mode-locked laser based on a laser dynamic establishment process and a control method. Background Art

[0002] Fourier domain mode-locked laser is one of the available high-speed frequency sweeping light sources, which can be applied to optical coherence tomography and is also widely used in optical radar, optical sensing, ultrafast pulse generation and optical device performance characterization. Fourier domain mode-locked laser is to add a long optical fiber as a delay line in the laser cavity so that each wavelength circulates in the cavity and reaches the frequency sweeping filter again, and the filter is just tuned to this wavelength to allow it to pass. Therefore, each wavelength does not need to be reconstructed from noise, and the frequency sweeping speed is not limited by the time for laser oscillation to be established, but is equal to the tuning speed of the filter, so a higher frequency sweeping speed can be achieved. Due to the combined effects of the dispersion and nonlinearity of the resonant cavity of the Fourier domain mode-locked laser, the noise of the optical amplifier, the frequency offset caused by the linewidth gain factor, the linewidth of the filter, the modulation frequency detuning and other factors, incoherent components will be generated, making the signal quickly unstable, and there is no strong correlation between the various frequency components, and the coherence and stability are poor.

[0003] In this regard, existing solutions usually use dispersion compensation (dispersion compensating fiber, dispersion shifted fiber, chirped grating), temperature stabilization control, feedback compensation, etc. to improve the coherence of Fourier domain mode-locked lasers. However, the above technical solutions require the use of expensive customized devices, which not only increases the complexity and cost of the laser, but also the devices are easily affected by the environment, making it difficult to ensure the long-term stability of the laser, and the coherence length of the laser is still not high.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a Fourier domain mode-locked laser and a control method based on a laser dynamic establishment process, so as to solve the problems that the existing technical solutions for improving the coherence of Fourier domain mode-locked lasers are highly complex and costly, and are easily affected by the environment and have low coherence.

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

[0007] A Fourier domain mode-locked laser based on a laser dynamic establishment process, comprising an optical amplifier for providing gain for a laser signal and modulating the intensity of the laser signal;

[0008] A first isolator and a second isolator for making the laser signal run unidirectionally;

[0009] A tunable filter for sweeping signal frequency control of the laser signal;

[0010] Delay optical fiber for buffering laser signals;

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

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

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

[0014] The 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 amount in the ring laser cavity exceeds the bandwidth range of the tunable filter.

[0015] According to a further configuration of the present invention, 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 discretizing the laser signal in the frequency domain.

[0016] According to a further configuration of the present invention, there are multiple optical amplifiers, and the multiple optical amplifiers are connected in series or in parallel.

[0017] According to a further configuration of the present invention, the Fourier domain mode-locked laser further includes: an optical circulator and a reflector; the optical circulator is connected to the delay optical fiber, and the reflector is connected to the delay optical fiber.

[0018] According to a further configuration of the present invention, 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 coupler or a free-space optical coupler; the delay fiber is one or more of any type of single-mode fiber or multi-mode fiber; and the polarization controller is one or more of an optical fiber in-line polarization controller or a free-space polarization controller.

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

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

[0021] When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, the optical amplifier is controlled to restart.

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

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

[0024] A first isolator and a second isolator for making the laser signal run unidirectionally;

[0025] A tunable filter for sweeping signal frequency control of the laser signal;

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

[0027] Delay optical fiber for buffering laser signals;

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

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

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

[0031] The 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 amount in the ring laser cavity exceeds the bandwidth range of the tunable filter.

[0032] According to a further configuration of the present invention, the Fourier domain mode-locked laser further comprises: a comb filter; the comb filter is used for discretizing the laser signal in the frequency domain.

[0033] A control method for a Fourier domain mode-locked laser based on the above-mentioned laser dynamic establishment process comprises:

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

[0035] When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, the intensity modulator is controlled to restart.

[0036] In a further configuration of the present invention, the step of controlling the arbitrary waveform generator to output the first control signal to drive the optical amplifier comprises:

[0037] The first control signal is pulse modulated to discretize the laser signal in the time domain.

[0038] The present invention provides a Fourier domain mode-locked laser and a control method based on a laser dynamic establishment process, which has the following beneficial effects:

[0039] The present invention controls the restart of the optical amplifier or intensity modulator when the dispersion in the ring laser cavity exceeds the bandwidth range of the tunable filter, thereby replacing the continuous gain intracavity signal by restarting the laser signal to counteract the residual dispersion in the cavity, thereby achieving high coherence swept-frequency laser output. Compared with conventional Fourier mode-locked lasers, no dispersion compensation technology is required, the scheme is simple, the requirements for the devices used in the laser are low, and no environmental control technology assistance is required. It has strong robustness and reduces costs, and can be applied to Fourier domain mode-locked lasers of any band. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary personnel in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

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

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

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

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

[0045] Figure 5 It is a flow chart of a method for controlling a Fourier domain mode-locked laser in one embodiment of the present invention.

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

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

[0048] Figure 8 It is a flow chart of a method for controlling a Fourier domain mode-locked laser in another embodiment of the present invention.

[0049] The marks in the accompanying drawings are: 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 invention provides a Fourier domain mode-locked laser and a control method based on a laser dynamic establishment process. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] In the embodiments and the scope of the patent application, unless the text specifically defines the article, "a", "an", "the" and "the" may also include plural forms. If there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0052] It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. 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 also be intermediate elements. In addition, the "connection" or "coupling" used herein can include wireless connection or wireless coupling. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

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

[0054] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0055] The laser has a laser cavity, that is, a resonant cavity. The function of the resonant cavity is to select light with a certain frequency and consistent direction for the highest priority amplification, and suppress light of other frequencies and directions. Any photon that does not meet the resonant frequency or moves along the axis of the resonant cavity cannot be amplified. Photons that meet the resonant frequency and move along the axis will continue to move forward in the cavity, and will continue to run back and forth in the annular cavity to produce oscillations. During the operation, they will continue to encounter excited particles and produce stimulated radiation. The photons will continue to multiply, forming a strong light beam with a consistent propagation direction and a stable relationship between frequency and phase in the cavity. This is a laser.

[0056] Fourier domain mode-locked laser is a device that obtains high-speed frequency-sweeping light source. Fourier mode-locked laser generally has two architectures, namely, the spatial structure based on block optical elements and the fiber architecture based on the fiber device structure. Among them, the mode-locked fiber laser can be divided into two types according to its structural cavity: linear cavity and ring cavity. The ring cavity refers to a ring-shaped cavity structure formed by connecting various optical devices to each other.

[0057] The inventors have found that after the Fourier domain mode-locked laser signal travels back and forth dozens of times in the ring resonator, a highly coherent swept-frequency laser signal can be established from the amplified spontaneous radiation, such as Figure 1 As shown in a, Figure 1 The horizontal axis in represents the number of round trips in the ring laser cavity, and the vertical axis represents the sampling point index. After the swept laser passes through the interferometer, stable interference fringes can be formed in the time domain, such as Figure 1 However, as the number of round trips of the laser signal in the cavity increases, Figure 1 As shown in c, incoherent components will be generated in the laser signal, significantly destroying the coherence of the laser. The speed at which incoherent components are generated is mainly affected by the total dispersion of the laser cavity, the frequency sweep speed, and the linewidth gain factor of the optical amplifier. This process will occur repeatedly until the laser trace is full of incoherent components, degrading the laser coherence length and signal-to-noise ratio. In this regard, existing solutions usually use dispersion compensation, temperature stability control, feedback compensation and other methods to improve the coherence of Fourier domain mode-locked lasers. However, the above technical solutions require the use of expensive customized devices, which not only increases the complexity and cost of the laser, but also the devices are easily affected by the environment, making it difficult to ensure the long-term stability of the laser, and the coherence length of the laser is still not high.

[0058] In response to the above technical problems, the present invention provides a Fourier domain mode-locked laser and control method based on the laser dynamic establishment process, which controls the optical amplifier or intensity modulator to restart when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, thereby replacing the continuous gain intracavity signal by restarting the laser signal to combat the residual dispersion in the cavity, thereby achieving high-coherence swept-frequency laser output. Compared with conventional Fourier mode-locked lasers, no dispersion compensation technology is required, the solution is simple, the requirements for the devices used in the laser are low, and no environmental control technology assistance is required. It has strong robustness and reduces costs, and can be applied to Fourier domain mode-locked lasers of any band.

[0059] Please also see Figure 2 and Figure 3 The present invention provides a preferred embodiment of a Fourier domain mode-locked laser based on a laser dynamic establishment process.

[0060] In some embodiments, Figure 1 As shown, the present invention provides a Fourier domain mode-locked laser based on a laser dynamic establishment process, which includes: an optical amplifier 1, a first isolator 2, a second isolator 3, an adjustable filter 4, a delay fiber 5, a coupler 6, a polarization controller 7 and an arbitrary waveform generator 8. Among them, the optical amplifier 1, the first isolator 2, the second isolator 3, the tunable filter 4, the delay 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 unidirectionally; the tunable filter 4 is used to perform frequency sweeping output signal frequency control on the laser signal; the delay fiber 5 is used to provide buffering for the laser signal; the coupler 6 is used to output the laser signal and maintain the laser signal oscillation 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 to the optical amplifier 1 and the tunable filter 4 respectively, and 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 is used to restart the optical amplifier 1 when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter 4. In this embodiment, the mode-locked laser is composed of a ring laser cavity formed by the arbitrary waveform generator 8 and the optical amplifier 1, the first isolator 2, the second isolator 3, the tunable filter 4, the delay 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 simultaneously trigger, drive and manage the tunable filter 4 and the optical amplifier 1, so that the arbitrary waveform generator 8 can periodically form wavelength scanning and gain switching in the ring laser cavity, wherein 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 as follows: the frequency v of the sinusoidal signal is selected according to the length L of the delay optical fiber 5, v=c / 2nL, where n is the refractive index of the optical fiber and c represents the speed of light. This selection can ensure that when each wavelength circulates in the cavity and reaches the tunable filter 4 again, the tunable filter 4 is tuned to this wavelength to allow it to pass through, so as to meet the dynamic filtering, wherein the amplitude voltage and bias voltage of the sinusoidal signal are selected according to the sweep range requirements of the tunable filter 4. The first control signal is the switching signal of the optical amplifier 1. The first control signal can be a periodic square wave signal. The periodic square wave signal can drive the optical amplifier 1 and control the optical amplifier 1 to be turned off or turned on again. In this way, the first control signal output by the arbitrary waveform generator 8 can realize the restart of the optical amplifier 1, and then the laser can be restarted.

[0062] The first isolator 2 and the second isolator 3 can realize the unidirectional operation of the laser signal and protect the optical amplifier 1 from the influence of reflected light and backscattered light. At the same time, adding an isolator to the ring laser can avoid the occurrence of optical resonance effect and ensure the flatness and consistency of the swept spectrum. It should be noted that the optical resonance effect requires a light path that can pass through both the forward and reverse directions. Assuming that its length is L, in the case of a resonance effect, the laser component whose optical frequency satisfies c / 2nL will be filtered out or enhanced. Both of these situations will cause the swept laser spectrum to be uneven and degrade the laser performance. The use of an isolator can block the light path passing in the reverse direction to avoid the 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 tunable filter 4 can be a mechanical or integrated tunable filter 4 based on the cooperation of the scanning lens and the grating and the control of piezoelectric ceramics, and the signal control is generated by the arbitrary waveform generator 8 to perform narrowband filtering on the optical signal. It should be noted that the connection sequence of 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 can be adjusted. Figure 2 This is just one of the connection methods.

[0063] In a specific implementation, the tunable 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 multiples. The optical amplifier 1 serves as the gain medium of 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 amount in the ring laser cavity exceeds the bandwidth range of the tunable filter 4, the arbitrary waveform generator 8 controls the optical amplifier 1 to restart, thereby restarting the laser operation before the incoherent components of the laser are generated, so as to counteract the generation of incoherent components caused by residual dispersion and nonlinearity in the ring laser cavity by restarting the laser signal, thereby improving the coherence and signal-to-noise ratio of the Fourier domain mode-locked laser.

[0064] Compared with conventional Fourier mode-locked lasers, the present invention can weaken the influence of residual dispersion in the laser cavity without any dispersion compensation technology, can greatly reduce the influence of dispersion on the dispersion in the cavity on the stable operation of the laser, better improve the coherence of the Fourier mode-locked laser, and overcome the limitations of the coherence of the Fourier mode-locked laser; compared with the existing Fourier mode-locked laser dispersion compensation scheme, it has lower requirements on the devices in the laser cavity, only uses the devices used in conventional Fourier domain mode-locked lasers, does not require the assistance of strict environmental control technology, has strong robustness, and reduces costs; compared with the existing Fourier mode-locked laser dispersion compensation scheme, this scheme is applicable to Fourier mode-locked lasers of any band, and is particularly suitable for building high-coherence Fourier mode-locked lasers in special bands such as one micron where dispersion compensation is difficult to achieve.

[0065] In some embodiments, the optical amplifier 1 is used as an actuator for the gain of the laser signal in the ring laser cavity and the laser restart. The optical amplifier 1 may be, but is not limited to, a semiconductor optical amplifier, a doped fiber amplifier, a Raman amplifier, or a parametric amplifier. The optical amplifier 1 may be formed by selecting different types of semiconductor materials, doped fibers, and pump light to form laser operation in different bands, and according to the laser cavity loss, the optical amplifier 1 may be set to one or more, and multiple optical amplifiers 1 may be connected in series or in parallel. For example, when a high laser cavity loss is required, a series connection is required, and when a high bandwidth requirement is required, a parallel connection is required.

[0066] In some embodiments, the coupler 6 can split the laser signal in different proportions, realize laser output in the ring laser cavity and maintain effective oscillation of the laser signal in the ring laser cavity. The coupler 6 can be a fiber coupler 6 or a free space optical coupler 6 based on mechanisms such as fiber fusion taper and waveguide splitting.

[0067] In some embodiments, the delay fiber 5 can provide a buffer for the laser signal in the ring laser cavity to prevent the laser signal from being re-established from amplified spontaneous radiation and to increase the frequency sweep speed. In one implementation, the delay fiber 5 can be any type of single-mode fiber or one or more of multi-mode fibers, that is, the delay fiber 5 can also be composed of any type of single-mode fiber and multi-mode fiber, and can achieve single unidirectional propagation.

[0068] Furthermore, if Figure 4 As shown, the Fourier domain mode-locked laser further includes: an optical circulator 11 and a reflector 12 ; the optical circulator 11 is connected to the delay optical fiber 5 , and the reflector 12 is connected to the delay optical fiber 5 .

[0069] Specifically, when bidirectional propagation delay is required, the delay optical fiber 5 can be combined with an optical circulator and the reflector to achieve bidirectional propagation delay. In some embodiments, the reflector can be a total reflection optical fiber ring, a reflector, a Faraday rotator reflector and other devices.

[0070] In some embodiments, the polarization controller 7 can realize the regulation of the polarization state of the laser 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 in-line polarization controller 7 based on different types of optical fibers such as a three-ring type, a double-ring type, and an extruded type, or a free-space polarization controller 7 composed of multiple glass slides.

[0071] In some embodiments, Figure 3 As shown, the Fourier domain mode-locked laser further includes: a comb filter 9; the comb filter 9 is arranged in the laser cavity, and the comb filter 9 is used to discretize the laser signal in the frequency domain.

[0072] In this embodiment, by adding a comb filter 9 in the ring laser cavity, the comb filter 9 can discretize the laser signal in the ring laser cavity in the frequency domain, and can use the narrower instantaneous line width of the comb filter 9 relative to the tunable filter 4 to allow the signal with a wavelength at the transmission peak of the tunable filter 4 to pass, 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, optical fiber ring, optical waveguide ring, etc.

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

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

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

[0076] In this embodiment, the arbitrary waveform generator can trigger, drive and manage the tunable filter and the optical amplifier at the same time, so that the arbitrary waveform generator can periodically form wavelength scanning and gain switching in the ring laser cavity, wherein the arbitrary waveform generator can calculate the switching period of the optical amplifier 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 optical amplifier to restart, thereby restarting the laser operation before the incoherent components of the laser are generated, so as to counteract the residual dispersion and nonlinearity in the ring laser cavity by restarting the laser signal, and improve the coherence and signal-to-noise ratio of the Fourier domain mode-locked laser.

[0077] In some embodiments, Figure 6 As shown, the present invention also provides another embodiment of the Fourier domain mode-locked laser, which includes: an optical amplifier 1, a first isolator 2, a second isolator 3, an adjustable filter 4, an intensity modulator 10, a delay fiber 5, a coupler 6, a polarization controller 7 and an arbitrary waveform generator 8. Wherein, 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 is used to provide gain for the laser signal; the first isolator 2 and the second isolator 3 are used to make the laser signal run unidirectionally; the tunable filter 4 is used to perform sweep signal frequency control on the laser signal; the intensity modulator 10 is used to modulate the intensity of the laser signal; the delay fiber 5 is used to provide buffering for the laser signal; the coupler 6 is used to output the laser signal and maintain the laser signal oscillating 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 to the intensity modulator 10 and the tunable filter 4 respectively, and the arbitrary waveform generator 8 is used to output a first control signal to drive the intensity modulator 10, output a second control signal to drive the tunable filter 4, and is used to control the intensity modulator 10 to restart when the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter 4.

[0078] In this embodiment, the arbitrary waveform generator 8 is used to simultaneously trigger and manage the adjustable filter 4 and the intensity modulator 10 in the cavity, so that they periodically form wavelength scanning and gain switching in the cavity. The adjustable filter 4 can realize the scanning of the laser frequency component in the cavity, wherein the scanning drive signal frequency corresponds to the cavity fundamental frequency or its multiples. The intensity modulator 10, as an actuator for laser restart, can realize laser restart and time domain discretization, and realize intensity modulation of the laser signal. The optical amplifier 1 serves as a gain device for the laser signal in the ring cavity. The purpose of the first isolator 2 and the second isolator 3 is to realize the unidirectional operation of the laser and to protect the optical amplifier 1 from the influence of reflected light and backscattered light. The delay fiber 5 is used to provide a buffer for the intracavity frequency sweep laser signal to prevent the laser signal from being re-established from amplified spontaneous radiation and to increase the frequency sweep speed. The coupler 6 is used to realize the intracavity laser output and maintain the effective oscillation of the laser in the cavity. The polarization controller 7 is used to control 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] Among them, the light intensity modulator 10 is used to realize the intensity modulation of the optical signal, and can be different types of optical modulators such as electro-optic modulator, acousto-optic modulator, magneto-optic modulator, semiconductor electro-absorption modulator, micromechanical optical switch, etc., or it can directly modulate the pump electrical signal or optical signal of the optical amplifier 1; the adjustable filter 4 can be a mechanical or integrated adjustable filter 4 based on the cooperation of the scanning lens and the grating and the control of piezoelectric ceramics, and the optical signal is narrow-band filtered by the signal control generated by the arbitrary waveform generator 8; the polarization controller 7 can be but not limited to different types of optical fiber online polarization controllers 7 based on three-ring type, double-ring type, extrusion type, etc., or a free space polarization controller 7 composed of multiple glass slides; the optical amplifier 1 can be but not limited to a semiconductor optical amplifier 1, a doped fiber amplifier, a Raman amplifier, and a parametric amplifier. Among them, the optical amplifier 1 can be formed by the selection of different types of semiconductor materials, doped optical fibers, and pump light to form laser operation in different bands, and according to the laser cavity loss, the optical amplifier 1 can be set to one or more, and the multiple optical amplifiers 1 are connected in series or in parallel. For example, when high laser loss is required, a series connection is required, and when high bandwidth requirements are required, a parallel connection is used; the coupler 6 can be an optical fiber coupler 6 or a free space optical coupler 6 based on mechanisms such as optical fiber melting cones and waveguide beam splitting; in one implementation, the delay optical fiber 5 can be any type of single-mode optical fiber or multi-mode optical fiber. One or more, that is, the delay optical fiber 5 can also be composed of any type of single-mode optical fiber and multi-mode optical fiber, which can realize single unidirectional 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 total reflection optical fiber ring, a reflector, a Faraday rotator reflector, and other devices.

[0080] In specific implementation, the arbitrary waveform generator 8 triggers and drives the adjustable filter 4 and the modulation intensity modulator 10 at the same time, and selects the switching cycle 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 during the establishment process. When the dispersion exceeds the filter bandwidth range, the high-coherence Fourier domain mode-locked laser signal is reestablished by switching the intensity modulator 10 to prevent the generation of incoherent components caused by dispersion and nonlinearity in the ring laser cavity, thereby improving the coherence and signal-to-noise ratio of the Fourier domain mode-locked laser. Compared with conventional Fourier mode-locked lasers, no dispersion compensation technology is required, the solution is simple, the requirements for the devices used in the laser are low, and no environmental control technology assistance is required. It has strong robustness and reduces costs, and can be applied to Fourier domain mode-locked lasers of any band.

[0081] In some embodiments, Figure 7As shown, the Fourier domain mode-locked laser further includes: a comb filter 9; the comb filter 9 is used to discretize the laser signal in the frequency domain.

[0082] In this embodiment, by adding a comb filter 9 in the ring laser cavity, the comb filter 9 can discretize the laser signal in the ring laser cavity in the frequency domain, and the narrower instantaneous line width of the comb filter 9 relative to the tunable filter 4 can be used to allow the signal with a wavelength at the transmission peak of the tunable filter 4 to pass, so as to optimize the coherence 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, optical fiber ring, optical waveguide ring, etc. It should be noted that if the intensity modulator 10 is used to discretize the laser signal in the time domain, then the pulse frequency driving the intensity modulator 10 should be synchronized with the frequency of the comb filter in the time domain discrete laser signal.

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

[0084] S100, controlling the arbitrary waveform generator to output a first control signal intensity modulator, and output a second control signal to drive the adjustable 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 this embodiment, the arbitrary waveform generator can simultaneously trigger, drive and manage 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, wherein 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, thereby restarting the laser operation before the incoherent components of the laser are generated, so as to counteract the residual dispersion and nonlinearity in the ring laser cavity by restarting the laser signal, and 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 steps of:

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

[0089] In this embodiment, a pulse signal is loaded onto the first control signal of the intensity modulator to discretize the laser signal in the time domain and synchronize the pulse frequency with the frequency of the comb filter, thereby improving the signal-to-noise ratio of the laser signal.

[0090] In summary, the present invention provides a Fourier domain mode-locked laser and a control method based on a laser dynamic establishment process. Based on the Fourier domain mode-locked laser dynamic establishment process, the intensity modulator or the optical amplifier is switched before the incoherent components of the laser are generated, and the laser operation is restarted to improve the coherence and signal-to-noise ratio of the Fourier domain mode-locked laser. It is mainly used to solve the problem of large residual dispersion of the Fourier domain mode-locked laser cavity and poor laser coherence, and does not require the introduction of customized devices or the use of strict constant temperature vibration isolation systems. The solution is simple and low cost.

[0091] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A Fourier domain mode-locked laser based on a laser dynamic establishment process, characterized in that: include: An optical amplifier for providing gain for a laser signal and modulating the intensity of the laser signal; A first isolator and a second isolator for making the laser signal run unidirectionally; A tunable filter for sweeping signal frequency control of the laser signal; Delay optical fiber for buffering laser signals; A coupler for outputting a laser signal and maintaining the laser signal oscillating in the cavity; A polarization controller for regulating the polarization state of a ring laser cavity; The optical amplifier, the first isolator, the second isolator, the tunable filter, the delay optical fiber, the coupler and the polarization controller form a ring laser cavity; The 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 amount 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 arranged in the laser cavity, and the comb filter is used to discretize the laser signal in the frequency domain.

3. The Fourier domain mode-locked laser based on the laser dynamic establishment process according to claim 1, characterized in that: There are multiple optical amplifiers, 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 optical fiber, and the reflector is connected to the time-delay optical 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 coupler or a free-space optical coupler; the delay fiber is one or more of any type of single-mode fiber or multi-mode fiber; 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 a laser dynamic establishment process according to any one of claims 1 to 5, characterized in that: include: Controlling the arbitrary waveform generator to output a first control signal to drive the optical amplifier, and output a second control signal to drive the adjustable filter; When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, the optical amplifier is controlled to restart.

7. A Fourier domain mode-locked laser based on a laser dynamic establishment process, characterized in that: include: An optical amplifier for providing gain to a laser signal; A first isolator and a second isolator for making the laser signal run unidirectionally; A tunable filter for sweeping signal frequency control of the laser signal; An intensity modulator for modulating the intensity of a laser signal; Delay optical fiber for buffering laser signals; A coupler for outputting a laser signal and maintaining the laser signal oscillating in the cavity; A polarization controller for regulating 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 optical fiber, the coupler and the polarization controller form a ring laser cavity; The 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 amount 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: Comb filter; the comb filter is used to discretize the laser signal in the frequency domain.

9. A control method for a Fourier domain mode-locked laser based on a laser dynamic establishment process according to claim 7 or 8, characterized in that: include: Controlling the arbitrary waveform generator to output a first control signal intensity modulator, and output a second control signal to drive the adjustable filter; When the dispersion amount in the ring laser cavity exceeds the bandwidth range of the tunable filter, the intensity modulator is controlled to restart.

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 optical amplifier comprises: The first control signal is pulse modulated to discretize the laser signal in the time domain.

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