Method for stable production of broadband tunable lasers and their frequency conversion devices

Abstract

The application discloses a method for stably preparing a nonlinear frequency conversion device and a corresponding wideband tunable laser, wherein duty cycle modulation is realized by deleting a specific position electrode distribution instead of precisely operating electrode width, so that the stability of the preparation process is greatly improved. In addition, by selecting, for example, magnesium-doped lithium niobate material to prepare the nonlinear frequency conversion device, a wideband optical window is ensured, by chirping the polarization lithium niobate along the light propagation direction, the frequency conversion spectrum is expanded, and by modulating the polarization duty cycle, the tuning curve is optimized, and the output power fluctuation is reduced.

Description

Technical Field

[0001] This invention relates to the field of lasers and frequency conversion devices, and in particular to a stable fabrication method for a broadband tunable laser and its frequency conversion device. Background Technology

[0002] Tunable lasers are indispensable devices in fields such as optical communication, industrial inspection, materials processing, and spectral analysis. Existing tunable laser technologies, such as external cavity tunable lasers (ECLs), utilize diffraction gratings, etalons, or Si-based microrings as mode-selection devices to choose the laser wavelength. However, these devices require precise adjustment using microelectromechanical systems (MEMS) and are complex and bulky. Distributed feedback (DFB) lasers offer high output power and strong frequency stability, and their output wavelength can be tuned by temperature control, with a temperature tuning coefficient of approximately 0.1 nm / ℃. However, considering that excessively high or low temperatures can significantly degrade laser performance, the operating temperature range of DFB lasers is generally limited to no more than 50℃, resulting in a limited tuning range of approximately 3-5 nm. The tuning range of DFB lasers can be extended through cascading, but this is costly and results in poor long-term stability. Distributed Bragg mirror (DBR) lasers offer low cost and high frequency stability, controlling the reflection wavelength of the DBR grating by changing the injection current. However, they do not include mechanisms such as the vernier effect for extending the tuning range, and their tuning range is generally limited to 5-10 nm. The tuning range of DBR lasers can be extended by designing superstructure gratings, but the process and packaging are extremely difficult, and the tuning process is complex.

[0003] Periodically polarized lithium niobate (PPLN) crystals / waveguides, fabricated using magnesium-doped lithium niobate (MgO:LN) material and prepared via external high-voltage polarization, are a type of nonlinear frequency conversion device. They support high-efficiency optical frequency conversion output within a 400-4500 nm optical transmission window, offering advantages such as fast response and compact structure. However, traditional PPLN devices have a fixed internal polarization period designed for a single operating wavelength to compensate for phase mismatch between the signal light and the frequency conversion light. Their conversion bandwidth is affected by the device length and the wavelength of the frequency conversion light. While the output wavelength can be adjusted by controlling the phase matching condition through temperature control, the tunable range is limited. In contrast, chirped polarized lithium niobate, building upon traditional PPLN devices, compensates for wideband phase mismatch by setting a continuously varying chirped polarization period, enabling continuous broadband optical nonlinear frequency conversion. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention discloses a method for stably fabricating nonlinear frequency conversion devices and corresponding broadband tunable lasers. The method achieves duty cycle modulation by replacing the width of precision operating electrodes with the deletion of electrode distributions at specific locations, significantly improving the stability of the fabrication process. Furthermore, the use of materials such as magnesium-doped lithium niobate to fabricate the nonlinear frequency conversion device ensures a broadband light transmission window; chirping and polarizing lithium niobate along the light propagation direction expands the frequency conversion spectrum; and optimizing the tuning curve by modulating the polarization duty cycle reduces output power fluctuations.

[0005] Specifically, the first aspect of the present invention relates to a stable fabrication method for a nonlinear frequency conversion device, which includes a polarization period determination step, a deletion electrode position determination step, and a device fabrication step.

[0006] The polarization period determination step is used to calculate the chirped polarization period distribution function ∧[x], x∈[0,L], of the nonlinear frequency conversion device in the optical transmission direction based on a 50% polarization duty cycle, where L is the length of the nonlinear frequency conversion device;

[0007] The step of determining the location of the deleted electrode is used to determine the location of the polarization electrode to be deleted based on the chirped polarization period distribution function ∧[x].

[0008] The device fabrication step is used to form polarization electrodes for the nonlinear frequency conversion device according to the chirped polarization period distribution function ∧[x] and the position of the polarization electrode to be deleted;

[0009] In the step of determining the location of the deleted electrode:

[0010] Apodization regions are respectively set at both ends of the nonlinear frequency conversion device, and the length of the apodization region is set. The apodization region includes a starting point located at the outermost end of the nonlinear frequency conversion device and an ending point closest to the center of the nonlinear frequency conversion device.

[0011] The number of polarization periods in the apodization region is determined based on the chirped polarization period distribution function ∧[x].

[0012] Within the number of polarization cycles in the apodization region, calculate the apodization region polarization electrode distribution that allows the equivalent polarization duty cycle to gradually change from 0% at the starting point to 50% at the ending point, and determine the position of the polarization electrode to be deleted based on the apodization region polarization electrode distribution.

[0013] Preferably, the length of the apodization region is set to 15% of the length L of the nonlinear frequency conversion device.

[0014] Preferably, the apodization polarization electrode distribution allows the equivalent polarization duty cycle to change linearly from 0% at the starting point to 50% at the ending point.

[0015] Preferably, the apodization region electrode distribution allows the conversion efficiency to change smoothly from 0% at the starting point to the maximum value at the ending point.

[0016] Preferably, the nonlinear frequency conversion device is prepared using a magnesium-doped lithium niobate material; or, the nonlinear frequency conversion device is prepared using a z-cut magnesium-doped lithium niobate thin film material.

[0017] Furthermore, in the polarization period determination step, the polarization period is determined based on the output center wavelength λ of the nonlinear frequency conversion device. C The chirped polarization periodic distribution function ∧[x] is determined by the expected output bandwidth, operating temperature, and length.

[0018] Furthermore, the polarization period determination step includes:

[0019] Sub-step one: The output center wavelength λ is determined based on the operating temperature and length of the nonlinear frequency conversion device. C The starting wavelength λ1 and the ending wavelength λ N Perform simulations to obtain the output wavelength λ for each wavelength. i and its corresponding signal light wavelength λ s and pump light wavelength λ p Effective mode refractive index N i N s and N p , where i is a natural number from 1 to N;

[0020] Sub-step two, based on the effective mode refractive index N obtained in sub-step one. i N s and N p Determine the output center wavelength λ C Corresponding polarization period Λ C And determine the polarization period span Λ L ;

[0021] Sub-step three: Set the initial polarization period to Λ1 = Λ C -Λ L / 2, the termination polarization period is set to Λ N =Λ C +Λ L / 2, Simulate and calculate the tuning curve bandwidth of the nonlinear frequency conversion device and compare it with the expected output bandwidth. If they differ, adjust the chirp span and re-simulate and calculate the tuning curve bandwidth until a definite initial polarization period ΛΛ1 and an ending polarization period ΛΛ are obtained. N ;

[0022] Sub-step four involves utilizing the determined initial polarization period Λ1 and final polarization period Λ N The chirp constant D was calculated. g =(2π / Λ) N -2π / Λ1) / (2*L);

[0023] Sub-step five utilizes the determined initial polarization period Λ1 and final polarization period Λ N and the chirp constant D g Determine the distribution function Λ[x] = (2π*Λ1) / (2π+Λ1*D). g *x).

[0024] In the process of converting nonlinear frequency to frequency doubling, Λ i =λ i / (N i -N s When the nonlinear frequency is converted into a sum frequency process, Λ i =1 / (N) i / λ i -N s / λ s -N p / λ p When the nonlinear frequency is converted into a difference frequency process, Λ i =1 / (|N s / λ s -N p / λ p |-N i / λ i ).

[0025] A second aspect of the present invention relates to a stable fabrication method for a broadband tunable laser, the broadband tunable laser comprising a signal source, a pump source, a nonlinear frequency conversion device, and a temperature control module; wherein,

[0026] The nonlinear frequency conversion device is prepared using the above-described stable preparation method;

[0027] The signal light source and pump light source are respectively configured to provide signal light and pump light for the nonlinear frequency conversion device; and,

[0028] The temperature control module is configured to control the temperature of the nonlinear frequency conversion device.

[0029] Preferably, the signal light source and / or pump light source is a tunable laser. Attached Figure Description

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A schematic diagram of the composition of a broadband tunable laser is shown.

[0033] Figure 2 The polarization period and inversion domain distribution in a typical chirped polarized device are schematically illustrated.

[0034] Figure 3 The polarization period and inversion domain distribution in conventional chirped polarized devices and apodized chirped polarized devices are schematically illustrated.

[0035] Figure 4 The theoretical tuning curves of a conventional chirped polarization device and an apodized chirped polarization device are schematically shown, wherein the polarization devices are suitable for tunable lasers in the 765-795 nm range.

[0036] Figure 5 The polarization period and inversion domain distribution of a delimited electrode type apodization chirped polarization device are schematically shown, in which a delimited electrode arrangement of every other electrode is used.

[0037] Figure 6 and 7 The measured tuning curves of a conventional chirped polarization device and a de-electrode type apodized chirped polarization device are schematically shown respectively, wherein the polarization devices are suitable for tunable lasers in the 765-795nm range. Detailed Implementation

[0038] In the following description, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the embodiments disclosed herein.

[0039] Figure 1 A schematic diagram of a broadband tunable laser is shown, which includes a signal source, a pump source, a nonlinear frequency conversion device, and a temperature control module.

[0040] The signal light source and the pump light source are used to provide signal light and pump light to the nonlinear frequency conversion device, respectively.

[0041] The signal and pump sources can be implemented using tunable lasers. The wavelengths of the signal and pump light can be selected based on the output wavelength requirements of the broadband tunable laser, corresponding to the nonlinear frequency conversion (frequency doubling / sum frequency / difference frequency) process. For example, for a 755-805nm broadband tunable laser, a 1510-1610nm tunable laser can be selected as the signal source for the frequency doubling process; for a 3137-3603nm broadband tunable laser, a 1510-1610nm tunable laser and a 1064nm laser can be selected as the signal and pump sources for the difference frequency process, respectively.

[0042] Nonlinear frequency conversion devices are used to realize nonlinear frequency conversion processes. In this invention, such nonlinear frequency conversion devices are realized using chirped polarized lithium niobate devices, wherein broadband nonlinear frequency conversion processes are achieved by chirping lithium niobate along the optical axis, thereby expanding the frequency conversion spectrum.

[0043] As an example, chirped polarized lithium niobate devices can be implemented using z-cut lithium niobate thin film materials. By designing a continuously chirped polarization period along the light propagation direction (i.e., the x-axis direction), the phase mismatch between the pump light and the output light can be compensated over a wide bandwidth, while ensuring that the maximum nonlinear coefficient d33 of lithium niobate participates in frequency conversion.

[0044] Figure 2 The polarization period and inversion domain distribution of a typical chirped polarized device are shown, where the positive and negative signs represent nonlinear coefficients whose signs are periodically reversed after polarization.

[0045] In a preferred example, the chirped polarized lithium niobate device can be fabricated using magnesium-doped lithium niobate material to ensure a broadband light transmission window.

[0046] In a periodically polarized device, the polarization duty cycle (i.e., inversion region / cycle length) for each cycle can be denoted as Dc, and its effective nonlinear coefficient can be expressed as dz∝sin(Dc*π). Therefore, in such a device... Figure 2 In the conventional chirped polarization device shown, the polarization duty cycle Dc is designed to be constant at 50% to obtain the maximum nonlinear coefficient. However, this causes significant fluctuations in the broadband conversion efficiency of the chirped polarization device. Therefore, to obtain a flat output spectrum, an apodized chirped polarization device design is proposed, which modulates the polarization duty cycle in the regions at both ends of the nonlinear frequency conversion device by adjusting the length of the inversion region in each polarization cycle.

[0047] Figure 3 The polarization period and inversion domain distribution of ordinary chirped polarized devices and apodized chirped polarized devices are schematically shown.

[0048] exist Figure 3In the example, 15% of the regions at each end of the apodized chirped polarizer are designated as apodization regions. Within each apodization region, the polarization duty cycle is modulated so that it linearly increases from 0% to 50% from both ends of the apodized chirped polarizer to the end of the apodization region.

[0049] Those skilled in the art will then understand that the frequency conversion spectrum (tuning curve) of an apodized chirped polarization device can be obtained by performing a Fourier transform on the effective nonlinear coefficients along the optical transmission direction over a wide bandwidth.

[0050] Figure 4 Simulated tuning curves of a conventional chirped polarization device and an apodized chirped polarization device suitable for tunable lasers in the 765-795nm range are shown. It can be seen that by modulating the polarization duty cycle distribution in the apodization region, the conversion efficiency jitter phenomenon of the broadband tuning curve of the device can be significantly improved, ultimately enabling the laser using this nonlinear frequency conversion device to obtain a flat output spectrum.

[0051] Theoretically, in conventional apodized chirped devices, the polarization duty cycle in the apodized region can be gradually varied from 0 to 50% from the device edge to the endpoint by precisely and continuously changing the electrode width in the light propagation direction, while maintaining a constant polarization duty cycle of 50% in the non-apodized region. However, in actual device fabrication, unstable factors such as electrode widening during polarization can lead to uncontrollable polarization duty cycles, typically with an error of ±5%. This error has a small impact on the non-apodized region but a significant impact on the effective nonlinear coefficient in the apodized region, thus affecting the frequency conversion efficiency. Consequently, the performance of the fabricated nonlinear frequency conversion device becomes unstable, meaning the actual effectiveness and repeatability of this fabrication process need improvement.

[0052] To address this issue, the inventors noticed through research that the essence of modulating polarization duty cycle is to reduce the frequency conversion efficiency of the corresponding region. Therefore, through further research, they proposed to equivalently modulate the polarization duty cycle in the apodization region by deleting the electrode arrangement at specific locations. This avoids unstable factors such as electrode broadening in existing processes, improves the stability of the fabrication process, and achieves the goal of reducing conversion efficiency and improving laser output efficiency jitter.

[0053] In the stable fabrication method of the nonlinear frequency conversion device proposed in this invention, the first step is to obtain the chirped polarization period distribution function Λ[x] of the nonlinear frequency conversion device in the optical transmission direction by means of the polarization period determination step.

[0054] In this invention, since the polarization duty cycle of the apodization region is equivalently modulated by deleting electrodes at specific locations, all electrodes can be designed with a polarization duty cycle of 50%, thereby greatly avoiding the impact of process errors on device performance.

[0055] Specifically, in the polarization period determination step, with a polarization duty cycle of 50%, the output center wavelength λ can first be determined based on the operating temperature and length of the nonlinear frequency conversion device (chirped polarized lithium niobate crystal / waveguide, etc.). C The starting wavelength λ1 and the ending wavelength λ N Perform simulations to obtain the output wavelength λ for each wavelength. i and its corresponding signal light wavelength λ s and pump light wavelength λ p Effective mode refractive index N i N s and N p Where i is a natural number from 1 to N. As those skilled in the art know, for nonlinear frequency conversion devices employing a frequency doubling process, it is possible to obtain only the corresponding effective mode refractive index N of the signal light and the output light. i and N s For nonlinear frequency conversion devices employing sum-frequency and difference-frequency processes, it is also necessary to obtain the effective mode refractive index N of the pump light. p .

[0056] To obtain the effective mode refractive index N corresponding to each output wavelength i N s and N p Based on this, the output center wavelength λ can be determined. C Corresponding polarization period Λ C And the polarization period span Λ corresponding to the start / end wavelength L As those skilled in the art will know, for the frequency doubling process, Λ i =λ i / (N i -N s For the sum-frequency process, Λ i =1 / (N) i / λ i -N s / λ s -N p / λ p For difference frequency processes, Λ i =1 / (|N s / λ s -N p / λ p |-N i / λ i The units for polarization period and wavelength are both μm.

[0057] Furthermore, the initial polarization period can be set to Λ1 = Λ C -Λ L / 2, the termination polarization period is set to Λ N =ΛC +Λ L / 2, Simulate the tuning bandwidth (i.e., laser output bandwidth) of the nonlinear frequency conversion device under its size and chirp period span, and compare it with the expected output bandwidth. If the simulated tuning bandwidth differs from the expected output bandwidth, the chirp width can be fine-tuned and the tuning bandwidth re-simulated until the determined polarization period start point ΛΛ1 and end point ΛΛ are finally obtained. N For example, if the bandwidth of the tuning curve obtained from the simulation is less than the expected output bandwidth, the chirp span can be slightly increased and the simulation can be repeated.

[0058] Therefore, based on the determined initial polarization period Λ1 and final polarization period Λ N Given the device length L, determine the chirp constant D. g =(2π / Λ) N -2π / Λ1) / (2*L), and then determine the polarization periodic distribution function Λ[x] of the nonlinear frequency conversion device in the optical transmission direction, Λ[x]=(2π*Λ1) / (2π+Λ1*D g *x), x∈[0,L].

[0059] Based on the obtained chirped polarization periodic distribution function ∧[x], the position of the polarization electrode to be deleted is determined by the electrode deletion position determination step, so as to determine the final polarization electrode distribution used for device fabrication.

[0060] The inventors noted that in the apodization region of a nonlinear frequency conversion device, if the polarization electrode is removed by skipping 'a' and then removing 'b', the conversion efficiency in the corresponding region will decrease to (a / (a+b))^2 of the original efficiency. For example, if the polarization electrode is removed by skipping 'one' and then removing 'two', the conversion efficiency in the corresponding region will decrease to approximately (1 / (1+2))^2 = 11.1% of the original efficiency; if the polarization electrode is removed by skipping 'one' and then removing 'one', for example, see [see section 1]. Figure 5 The polarization period and inversion domain distribution of the electrode-removed apodization chirped polarization device shown in the figure reduce the conversion efficiency of the corresponding region to approximately (1 / (1+1))^2 = 25% of the original. If the polarization electrodes are removed in a 3-for-4 manner, the conversion efficiency of the corresponding region decreases to approximately (4 / (4+3))^2 = 32.6% of the original. Therefore, the frequency conversion efficiency of the corresponding region can be reduced by removing specific polarization electrodes, thereby achieving equivalent modulation of the polarization duty cycle of the corresponding region, and realizing the required apodization region design without modulating the polarization electrode width.

[0061] Specifically, in the step of determining the location of the deleted electrode, the length L1 of the apodization region can be set first, for example, L1 = a% * L. As those skilled in the art know, apodization regions are provided at both ends of the nonlinear frequency conversion device, and each apodization region includes a starting point located at the outermost end of the nonlinear frequency conversion device and an ending point closest to the center of the nonlinear frequency conversion device.

[0062] At this point, the number of polarization periods in the apodization region can be determined based on the chirped polarization period distribution function Λ[x].

[0063] Then, based on the above formula for calculating the equivalent conversion efficiency of the apodization region for the electrode to be deleted, the distribution of polarized electrodes in the apodization region can be calculated, allowing the equivalent polarization duty cycle to gradually change from 0% at the start of the apodization region to 50% at the end of the apodization region (that is, the conversion efficiency gradually changes from 0% at the start to the maximum value at the end of the apodization region along the device edge towards the center, with the theoretical maximum value being 100%). Thus, the location of the polarized electrode to be deleted can be determined.

[0064] Preferably, the polarization electrode distribution in the apodization region allows the corresponding change curve to be a smooth curve, for example, changing in a linear manner.

[0065] According to the present invention, the corresponding tuning curve can be calculated based on the equivalent duty cycle distribution of the deleted electrode, allowing for more detailed optimization of the apodization region length and duty cycle modulation method to address the fluctuations in conversion bandwidth and broadband efficiency. Theoretically, the longer the apodization region length, the narrower the conversion bandwidth and the lower the fluctuation in broadband efficiency.

[0066] Therefore, the polarization electrode distribution for the final nonlinear frequency conversion device can be formed based on the chirped polarization periodic distribution function Λ[x] and the position of the polarization electrode to be removed, thereby fabricating the nonlinear frequency conversion device by applying a voltage signal to the polarization electrode in the device fabrication step.

[0067] Figure 6 and 7 The measured tuning curves of a conventional chirped polarization device and a de-electrode apodization chirped polarization device suitable for tunable lasers in the 765-795nm range are schematically shown respectively. It can be seen that the fabrication process of the de-electrode apodization chirped device proposed in this invention is stable and yields excellent results.

[0068] By applying the nonlinear frequency conversion device prepared by the above-described stable fabrication method to a broadband tunable laser, a tunable laser with adjustable bandwidth and a flat spectrum, allowing for arbitrary wavelengths within the 400-4500 nm range, can also be stably fabricated. Considering that temperature affects the refractive index of lithium niobate material, thus causing fluctuations in conversion efficiency, a temperature control module can be used to ensure that the nonlinear frequency conversion device operates under isothermal conditions.

[0069] In summary, the fabrication method of the nonlinear frequency conversion device and broadband tunable laser proposed in this invention ensures a broadband light transmission window by using materials such as magnesium-doped lithium niobate, extends the frequency conversion spectrum by chirping and polarizing lithium niobate along the light propagation direction, and reduces output power fluctuations by optimizing the tuning curve through modulation of the polarization duty cycle. Most importantly, duty cycle modulation is achieved by deleting electrode distributions at specific locations instead of using precise operating electrode widths, which greatly improves the stability of the fabrication process. Therefore, this invention provides a stable fabrication method for the nonlinear frequency conversion device and broadband tunable laser.

[0070] Although the present invention has been described above with reference to the accompanying drawings and specific embodiments, those skilled in the art will readily recognize that the above embodiments are merely exemplary and used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A stable fabrication method for a nonlinear frequency conversion device, comprising a polarization period determination step, an electrode removal position determination step, and a device fabrication step; The polarization period determination step is used to calculate the chirped polarization period distribution function of the nonlinear frequency conversion device in the optical transmission direction based on a 50% polarization duty cycle. X∈[0,L], where L is the length of the nonlinear frequency conversion device; The step of determining the location of the deleted electrode is based on the chirped polarization periodic distribution function. Determine the location of the polarization electrode to be deleted; The device fabrication step is used to determine the chirped polarization period distribution function. The positions of the polarization electrodes to be removed are used to form polarization electrodes for the nonlinear frequency conversion device to fabricate the nonlinear frequency conversion device; in, In the step of determining the location of the deleted electrode: Apodization regions are respectively set at both ends of the nonlinear frequency conversion device, and the length of the apodization region is set. The apodization region includes a starting point located at the outermost end of the nonlinear frequency conversion device and an ending point closest to the center of the nonlinear frequency conversion device. According to the chirped polarization periodic distribution function Determine the number of polarization periods within the apodization region; Within the number of polarization cycles in the apodization region, calculate the apodization region polarization electrode distribution that allows the equivalent polarization duty cycle to gradually change from 0% at the starting point to 50% at the ending point, and determine the position of the polarization electrode to be deleted based on the apodization region polarization electrode distribution.

2. The stable fabrication method of the nonlinear frequency conversion device as described in claim 1, wherein, The length of the apodization region is set to 15% of the length L of the nonlinear frequency conversion device.

3. The stable fabrication method of the nonlinear frequency conversion device as described in claim 1, wherein, The apodization polarization electrode distribution allows the equivalent polarization duty cycle to change linearly from 0% at the starting point to 50% at the ending point.

4. The stable fabrication method of the nonlinear frequency conversion device as described in claim 1, wherein, The electrode distribution in the apodization region allows the conversion efficiency to change smoothly from 0% at the starting point to the maximum value at the ending point.

5. The stable fabrication method of the nonlinear frequency conversion device as described in claim 1, wherein, The nonlinear frequency conversion device is prepared using magnesium-doped lithium niobate material; or, the nonlinear frequency conversion device is prepared using z-cut magnesium-doped lithium niobate thin film material.

6. The stable fabrication method of the nonlinear frequency conversion device as described in claim 1, wherein, In the polarization period determination step, the output center wavelength λ of the nonlinear frequency conversion device is used as a reference. C The chirped polarization periodic distribution function is determined by the expected output bandwidth, operating temperature, and length. .

7. The stable fabrication method of the nonlinear frequency conversion device as described in claim 6, wherein, The polarization period determination step includes: Sub-step one: The output center wavelength λ is determined based on the operating temperature and length of the nonlinear frequency conversion device. C The starting wavelength λ1 and the ending wavelength λ N Perform simulations to obtain the output wavelength λ for each wavelength. i and its corresponding signal light wavelength λ s and pump light wavelength λ p Effective mode refractive index N i N s and N p , where i is a natural number from 1 to N; Sub-step two, based on the effective mode refractive index N obtained in sub-step one. i N s and N p Determine the output center wavelength λ C Corresponding polarization period And determine the range of polarization period. ; Sub-step three: Set the initial polarization period to = - / 2, the termination polarization period is set to = + / 2, Simulate and calculate the tuning curve bandwidth of the nonlinear frequency conversion device and compare it with the expected output bandwidth. If they differ, adjust the chirp span and re-simulate and calculate the tuning curve bandwidth until a definite initial polarization period is obtained. and termination of polarization period ; Sub-step four: Utilize the determined initial polarization period and termination of polarization period The chirp constant was calculated. =(2π / -2π / ) / (2*L); Sub-step five: Utilize the determined initial polarization period and termination of polarization period and the chirp constant Determine the distribution function =(2π* ) / (2π+ * * ).

8. The stable fabrication method of the nonlinear frequency conversion device as described in claim 7, wherein, During the process of converting a nonlinear frequency to a frequency harmonic... =λ i / (N i -N s When the nonlinear frequency is converted into a sum frequency process, =1 / (N i / λ i -N s / λ s -N p / λ p When the nonlinear frequency is converted into a difference frequency process, =1 / (|N s / λ s -N p / λ p |-N i / λ i ).

9. A method for the stable fabrication of a broadband tunable laser, wherein the broadband tunable laser comprises a signal source, a pump source, a nonlinear frequency conversion device, and a temperature control module; wherein, The nonlinear frequency conversion device is prepared using the stable preparation method described in any one of claims 1-8; The signal light source and the pump light source are respectively configured to provide signal light and pump light for the nonlinear frequency conversion device; as well as, The temperature control module is configured to control the temperature of the nonlinear frequency conversion device.

10. The stable fabrication method of the broadband tunable laser as described in claim 9, wherein, The signal light source and / or pump light source are tunable lasers.

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