An ultrafast fiber laser

Abstract

The present application provides an ultrafast fiber laser, which mainly consists of a seed source for outputting MHz-level repetition rate pulses, an adjustable GHz pulse cluster repetition rate enhancement module, an amplification optical path module and a control module. The adjustable GHz pulse cluster repetition rate enhancement module mainly includes: a 50:50 optical coupler, a section of single-mode passive optical fiber of a specific length, an adjustable optical delay line, a circulator, a coupler / wavelength division multiplexer, a pump source, a section of single-mode active optical fiber, and two acousto-optic modulators or electro-optic modulators. The ultrafast fiber laser of the present application adopts a conventional MHz-level ultrafast fiber laser, which can realize an ultrafast laser light source of adjustable GHz-level pulse clusters, so as to be used in processing fields with high processing precision requirements, such as achieving system stability, controllable depth, higher adjustable space, and smooth inner wall glass drilling and other fields.

Description

Technical Field

[0001] The present application relates to the field of laser technology, in particular to an ultrafast fiber laser, and more specifically to a high repetition rate, GHz ultrafast fiber laser. Background Art

[0002] The repetition rate (RPR) describes the number of pulses a laser can output per unit time. For laser processing, a higher repetition rate means more laser energy interacting with the material per unit time. This allows the laser to ablate the material more quickly, effectively improving the efficiency of the process. Furthermore, by tuning the laser, the operator can precisely control the speed and state of the process, ensuring overall quality.

[0003] Although high-repetition-rate lasers have extremely bright application prospects in micromachining applications such as flexible circuit boards, precision parts, and micro-nanostructures, they also have unresolved technical defects: when the ablation threshold of the processed substrate is lower than the energy of a single laser pulse, the surface of the substrate will be damaged due to absorbing excessive energy, and will manifest in the form of cracks, burrs, etc.

[0004] In the long history of laser processing, many scholars have conducted their own research on the mode of laser output pulses and obtained many interesting results. Among them, the "burst mode" is a very novel and practical one. In essence, the burst mode characterizes the time domain transmission of ultrafast laser pulse clusters. In this mode, the pulses are no longer output at fixed time intervals, but are divided into pulse clusters consisting of multiple pulses by a controllable optical switch device, thereby achieving the expected indicators of pulse cluster output. Its specific output form is as follows: Figure 1 Compared to the high-repetition-rate output mode, which emits laser pulses at fixed time intervals, the Burst mode can reduce the number of pulses impacting the substrate per unit time while maintaining the average laser output power. This reduces damage to the substrate surface caused by thermal effects, thereby ensuring processing quality.

[0005] However, the above-mentioned Burst mode requires the use of a GHz light source system, which is difficult and expensive to implement. Currently, conventional repetition-rate ultrafast fiber lasers are basically at the MHz level, which cannot guarantee processing quality in areas with higher processing precision requirements and is difficult to promote on a large scale in the industry.

[0006] Based on this, it is necessary to apply for an ultrafast fiber laser, using a conventional MHz-level ultrafast fiber laser to realize an ultrafast laser light source with adjustable GHz-level pulse clusters, in order to solve the current defects in areas with higher processing precision requirements. Summary of the Invention

[0007] The purpose of this application is to provide an ultrafast fiber laser, which uses a conventional MHz-level ultrafast fiber laser to realize an ultrafast laser light source with adjustable GHz-level pulse clusters, so as to be used in processing fields with high processing precision requirements, such as achieving system stability, depth control, higher adjustable space, and smooth inner wall glass drilling.

[0008] To solve the problems raised in the above background technology.

[0009] To achieve the above objectives, this application provides the following technical solutions:

[0010] The present application provides an ultrafast fiber laser, which mainly comprises a seed source (Seed) for outputting MHz-level repetition rate pulses, an adjustable GHz pulse cluster repetition rate enhancement module, an amplification optical path module and a control module.

[0011] The seed source in this application has a pulse repetition frequency f in MHz and an output power generally in the mW range. It also has an SMA adapter that can output a repetition frequency electrical signal synchronized with the optical pulses, which is transmitted to a control module that can use a field programmable gate array (FPGA) mode.

[0012] The main feature of the ultrafast fiber laser of the present application is that it has an adjustable GHz pulse cluster repetition rate enhancement module, which mainly includes: a 50:50 optical coupler (OC), a single-mode passive fiber (SMF) of a specific length, an adjustable optical delay line (VODL), a circulator, a coupler / wavelength division multiplexer (WDM), a pump source (Pump), a single-mode active fiber, and two acousto-optic modulators (AOM) or electro-optic modulators (EOM).

[0013] The working principle of the ultrafast fiber laser of the present application is as follows: the optical pulse output end of the seed source is fused with the first port of a 50:50 splitter coupler, and then the output pulse of the seed will be equally divided into two equal parts and output from the second port and the third port respectively. The output pulse of the third port enters the delay loop, passes through a certain length of single-mode passive optical fiber and an adjustable optical delay line, enters the circulator from the fifth port of the circulator, and is output from the sixth port of the circulator. After passing through the pump source, coupler, and single-mode active optical fiber, it enters the circulator from the sixth port of the circulator again and is output from the seventh port of the circulator. Then, it passes through an acousto-optic / electro-optic modulator and enters the 50:50 splitter coupler from the eighth port, and is once again equally divided into two equal parts and output from the third port and the fourth port respectively. The above process is repeated.

[0014] The ultrafast fiber laser of the present application also includes a chirped fiber Bragg grating (CFBG), which is located behind the single-mode active optical fiber and constitutes a double-pass compensation amplification optical path module for compensating for the losses generated by various components in the loop, such as the adjustable optical delay line, the circulator, and the first acousto-optic / electro-optic modulator. The compensated amplified pulse enters the circulator from the sixth port of the circulator to prevent the energy of the rear pulse from continuously attenuating compared to the energy of the front pulse.

[0015] The main feature of the ultrafast fiber laser of the present application is that it has an adjustable GHz pulse cluster repetition rate enhancement module, through which the adjustable GHz pulse cluster repetition rate enhancement of the ultrafast fiber laser is achieved.

[0016] An adjustable optical delay line is added to the delay loop of the ultrafast fiber laser of the present application so that the optical path length of the delay loop can be precisely controlled, thereby precisely controlling the time delay.

[0017] Introduction to the implementation principle of high repetition rate pulse cluster output:

[0018] Given a seed source with a known pulse repetition rate of f and a period of T1 = 1 / f, its synchronized repetition rate signal is transmitted to the control module via its own SMA connector. The control module controls the first and second acousto-optic modulators to generate a modulation signal synchronized with the seed source with a fixed time delay, selecting the desired pulse cluster and suppressing other undesired pulse clusters. The resulting pulse clusters are the desired high-repetition-rate pulse clusters, which undergo multiple stages of amplification and are converted into high-energy pulsed lasers suitable for practical processing applications.

[0019] The chirped fiber Bragg grating (CFBG) in the loop is not only used to reflect the signal light, but also can be used to compensate for the dispersion generated by the pulse in a single cycle, so as to ensure that the dispersion of the pulses in the superimposed pulse cluster output is consistent, so that the pulse width and subsequent amplification process remain consistent.

[0020] This application achieves the effect of using a conventional MHz-level ultrafast fiber laser to realize an ultrafast laser light source with adjustable GHz-level pulse clusters by adding an adjustable GHz-level pulse cluster repetition rate enhancement module. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions of the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0022] Figure 1 Schematic diagram of the pulse train output form of existing ultrafast fiber lasers;

[0023] Figure 2 This is a schematic diagram of the first structure of the ultrafast fiber laser provided in this application;

[0024] Figure 3 Schematic diagram of the pulse train output form of the ultrafast fiber laser provided in this application;

[0025] Figure 4 This is a schematic diagram of the structure of the adjustable optical delay line provided in this application.

[0026] Figure 1: Seed source, 2: Spectral coupler, 3: Single-mode passive optical fiber, 4: Adjustable optical delay line, 5: Circulator, 6: Pump source, 7: Wavelength division multiplexer, 8: Single-mode active optical fiber, 9: Chirped fiber Bragg grating, 10: First acousto-optic modulator, 11: Second acousto-optic modulator, 12: Control module, 41: Input unit, 42: Reflection unit, 43: Adjustable range, 44: Output unit. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the embodiments described are only part of the embodiments of the present application and are not intended to limit the scope of the rights of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0028] See also Figure 2 , Figure 2This is a first structural diagram of the ultrafast fiber laser provided in this application. The ultrafast fiber laser mainly comprises a seed source 1 for outputting MHz-level repetition rate pulses, an adjustable GHz pulse cluster repetition rate enhancement module, a compensation amplification optical path module and a control module 12.

[0029] The seed source in this application can be a commercially available seed source 1 purchased from outside, which generally has a pulse repetition frequency f of MHz and an output power of mW level. It also has an SMA adapter to output a repetition frequency electrical signal synchronized with the optical pulse, and the signal is transmitted to the control module 12.

[0030] The main feature of the ultrafast fiber laser of the present application is that it has an adjustable GHz pulse cluster repetition rate increasing module, which mainly includes: a 50:50 optical coupler 2, a section of single-mode passive optical fiber 3 of a specific length, an adjustable optical delay line 4, a circulator 5, a wavelength division multiplexer 7, a pump source 6, a section of single-mode active optical fiber 8, and two acousto-optic modulators or electro-optic modulators. This embodiment uses a first acousto-optic modulator 10 (AOM1) and a second acousto-optic modulator 11 (AOM2) as the acousto-optic modulator combination.

[0031] The working principle of the ultrafast fiber laser of the present application is as follows: the optical pulse output end of the seed source 1 is fused with the first port of a 50:50 splitter coupler 2, and then the output pulse of the seed source 1 will be divided into two equal parts and output from the second port and the fourth port of the splitter coupler 2 respectively. The output pulse of the fourth port enters the delay loop, passes through a certain length of single-mode passive optical fiber 3, an adjustable optical delay line 4, enters the circulator 5 from the fifth port of the circulator 5, and then outputs from the sixth port of the circulator 5, and passes through the delay loop of the circulator 5. After passing through the pump source 6, wavelength division multiplexer 7, and single-mode active optical fiber 8, the light enters the circulator 5 from its sixth port and is output from its seventh port. It then passes through the acousto-optic / electro-optic modulator 10 and enters the 50:50 optical splitting coupler 2 from its third port. The light is then split into two equal parts and output from the second and fourth ports, respectively. The light pulse output from the second port then passes through the second acousto-optic / electro-optic modulator 11 and is output. The pulse output from the fourth port enters the delay loop again, and the above process repeats.

[0032] In a preferred embodiment, the ultrafast fiber laser further includes a chirped fiber Bragg grating 9, which is located behind the single-mode active fiber 8 and constitutes a double-pass compensation amplification optical path module for compensating for the losses generated by various components in the loop, such as the adjustable optical delay line 4, the circulator 5, and the first acousto-optic / electro-optic modulator 10. The compensated amplified pulse enters the circulator 5 from the sixth port of the circulator 5.

[0033] See also Figure 3 , Figure 3 This is a schematic diagram of the pulse train output form of the ultrafast fiber laser provided by the present application. The ultrafast fiber laser of the present application achieves adjustable GHz pulse cluster repetition rate improvement of the ultrafast fiber laser through an adjustable GHz pulse cluster repetition rate improvement module. The principle of adjustable GHz pulse cluster repetition rate improvement of the ultrafast fiber laser of the present application is as follows: the seed source 1 outputs periodic pulses with a repetition rate of f, T1 = 1 / f, and the position of the adjustable optical delay line 4 is adjusted, thereby changing the length of the single-mode passive optical fiber 3 in the loop, so that the pulse repetition period in the delay loop is T0. At this time, the light pulse generated by the seed source 1 and the light pulse output through the delay loop are superimposed to generate a time delay of T6 = |T0-T1|, where T6 is the repetition period of the pulse cluster. The length of the delay loop can be calculated by the formula T6 = |T0-(n*Lall) / c| through the time delay T6, where n is the average refractive index of the fiber core, c is the speed of light in vacuum, and Lall is the length of the single-mode passive fiber 3. An initial pulse cluster repetition rate f can be obtained by increasing or decreasing the length of the single-mode passive fiber 3. r , f r =1 / T6, generally, in order to obtain a pulse cluster repetition rate f of about 1 GHz r , then the value of T6 needs to be controlled close to 1ns. If the value of T6 is less than 1ns, the pulse cluster repetition frequency f r will be greater than 1 GHz. That is, in practical applications, according to the pulse cluster repetition frequency f r The value of T6 should be designed according to the specific needs.

[0034] See also Figure 4 , Figure 4 This is a schematic diagram of the structure of the adjustable optical delay line provided in the present application. The adjustable optical delay line 4 is added to the delay loop of the ultrafast fiber laser of the present application so that the ultrafast fiber laser can accurately control the optical path of the delay loop, thereby accurately controlling the delay T6. The adjustable optical delay line 4 includes an input part 41, a reflector 42, an adjustable range 43 and an output part 44. The reflector 42 and the adjustable range 43 are fixedly connected, and the output part 44 can be driven to move horizontally together by the translation of the adjustable range 43. The matching design of the two reflecting surfaces of the input part 41, the output part 44 and the reflector 42 makes the input light and the output light remain in a parallel relationship during the translation process. Due to the adjustability of the adjustable optical delay line 4, the pulse cluster has an adjustable repetition rate.

[0035] In an optional solution, the adjustable range 43 can be manually rotated to move horizontally, thereby driving the output part 44 to move horizontally. Alternatively, the adjustable range 43 can be controlled to move horizontally by an electrically controlled fine-tuning mechanism.

[0036] In a preferred solution, in the initial adjustment, the adjustable optical delay line 4 is controlled to be in the middle position of the adjustable range 43, which can flexibly meet the adjustment requirements of different high repetition rate pulse clusters required by the process and expand the scope of application.

[0037] Pulse repetition rate f within a pulse cluster r Example of adjustable range: Assuming that the adjustable range of the adjustable optical delay line 4 is ΔT, the initial position of the adjustable optical delay line 4 is adjusted to the middle position of the range so that it has nearly equal upper and lower adjustment ranges (±ΔT / 2), and by adjusting the length of the initial single-mode passive optical fiber 3, T6 is close to ΔT / 2, then the pulse repetition rate f in the pulse cluster is r The theoretical adjustable range is: (+∞, 1 / ΔT), and the upper limit of the actual adjustable pulse cluster repetition rate is limited by the pulse width of the initial optical pulse.

[0038] For example, if ΔT = 10 ns, the theoretical adjustable range of the pulse repetition frequency within a pulse cluster is (+∞, 100 MHz).

[0039] Introduction to the implementation principle of high repetition rate pulse cluster output:

[0040] See also Figure 3 It is known that the output pulse repetition frequency of the seed source 1 is f and the period is T1=1 / f. The synchronous repetition frequency signal output by the seed source 1 is transmitted to the control module 12 through its own SMA adapter. The control module 12 controls the first acousto-optic modulator 10 and the second acousto-optic modulator 11 to generate a modulation signal synchronized with the seed source 1 with a fixed delay T2. The repetition frequency of the modulation signal and the duty cycle within one period are determined according to the following relationship:

[0041] T3+T4 is the length of one cycle of the first AOM 10. T3 is the duration of the high-level cycle of the first AOM 10, indicating the length of time the delay loop is open within a single modulation cycle of the first AOM 10. Generally, T3 is N times the length of the ultrafast seed source period T, which is used to control the maximum number of pulses in the delayed superposition pulse cluster circulated in the loop, with the number of superimposed pulses in the maximum pulse cluster being N. T4 is used to terminate the pulse superposition cycle within a single modulation cycle of the first AOM 10. T4 is M times the length of the ultrafast seed source period T, where M must be greater than 1 to achieve an effective cycle cut-off function. Once this condition is met, after the modulation signal of a single first AOM 10 begins, the number of superimposed pulses in the loop will increase from 1 to N, and the cycle will continue. Therefore, the total length of a modulation signal cycle of the first AOM 10 is (N+M)*T, and the corresponding repetition frequency is 1 / ((N+M)*T);

[0042] When N=6, the corresponding 2-channel output pulse sequence is as follows Figure 3 As shown;

[0043] The second AOM 11 selects and outputs the desired superimposed pulse cluster. The fixed time delay between the rising edge of its modulation signal and the signal from the first AOM 10 is T5, and T5 can be adjusted within the range of (0, (N-1)*T). The high-level duration within a single cycle of the second AOM 11 is T1, which is the pulse period of a single ultrafast seed source. Therefore, the second AOM 11 can select the desired pulse cluster and suppress other undesired pulse clusters.

[0044] The pulse cluster output by the second acousto-optic modulator 11 is the desired high-repetition-rate pulse cluster optical pulse, which will then undergo multiple stages of amplification and be converted into a high-energy pulse laser that can be used for practical processing applications.

[0045] The chirped Bragg grating 9 in the loop is not only used to reflect the signal light, but also can be used to compensate for the dispersion generated by the pulse in a single cycle to ensure that the dispersion of the pulses in the superimposed pulse cluster output is consistent, so that the pulse width and subsequent amplification process remain consistent.

[0046] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device comprising a series of elements are inherent to the elements. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements. In addition, the above-mentioned technical solutions provided in the embodiments of the present application are not described in detail in accordance with the corresponding technical solutions in the prior art to achieve the same principle, so as to avoid excessive elaboration.

[0047] Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core ideas of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, various improvements and modifications may be made to the present application, as well as combinations of the various embodiments in the present application. Such improvements, modifications, and combinations also fall within the scope of protection of the claims of the present application.

Claims

1. An ultrafast fiber laser, characterized in that , comprising a seed source (1) for outputting MHz-level repetition rate pulses, an adjustable GHz pulse cluster repetition rate enhancement module, a compensation amplification optical path module and a control module (12); The seed source (1) has a pulse repetition frequency f of MHz, an output power of mW level, and an SMA adapter capable of outputting a repetition frequency electrical signal synchronized with the optical pulse, and the signal is transmitted to the control module (12); The adjustable GHz pulse cluster repetition rate increasing module comprises: a 50:50 split optical coupler (2), a section of single-mode passive optical fiber (3), an adjustable optical delay line (4), a circulator (5), a pump source (6), a wavelength division multiplexer (7), a section of single-mode active optical fiber (8), and two acousto-optic modulators or electro-optic modulators; The compensation amplification optical path module includes a chirped Bragg fiber grating (9), and the chirped Bragg fiber grating (9) is located behind the single-mode active optical fiber (8); The optical pulse output end of the seed source (1) is fused with the first port of a 50:50 split optical coupler (2), and then the output pulse of the seed source (1) is divided into two equal parts and output from the second port and the fourth port of the split optical coupler (2), respectively. The output pulse of the fourth port enters the delay loop, passes through a certain length of single-mode passive optical fiber (3), an adjustable optical delay line (4), enters the circulator (5) from the fifth port of the circulator (5), and is output from the sixth port of the circulator (5), passes through the pump source (6), and the wavelength division multiplexer ( 7), a single-mode active optical fiber (8), a chirped fiber Bragg grating (9), and then enters the circulator (5) from the sixth port of the circulator (5), and then outputs from the seventh port of the circulator (5), then passes through the first acousto-optic modulator (10), and then enters the 50:50 optical splitting coupler (2) from the third port, and is once again divided into two equal parts, and output from the second port and the fourth port respectively. The optical pulse output from the second port is output after passing through the second acousto-optic modulator (11), and the pulse output from the fourth port enters the delay loop again, and the above process is repeated.

2. The ultrafast fiber laser according to claim 1, characterized in that The first acousto-optic modulator (10) and the second acousto-optic modulator (11) both use acousto-optic modulators as an acousto-optic modulator combination.

3. The ultrafast fiber laser according to claim 1, characterized in that The seed source (1) outputs a periodic pulse with a repetition frequency of f, T1 = 1 / f, and the position of the adjustable optical delay line (4) is adjusted, thereby changing the length of the single-mode passive optical fiber (3) in the loop, so that the pulse repetition period in the delay loop is T0, so that the optical pulse generated by the seed source (1) and the optical pulse output through the delay loop are superimposed to generate a time delay of T6 = |T0-T1|, where T6 is the repetition period of the pulse cluster; By increasing or decreasing the length of the single-mode passive optical fiber (3), the repetition rate f of an initial pulse cluster is controlled. r , f r =1 / T6, the length of the delay loop is calculated using the formula T6=|T0-(n*Lal l) / c|, where n is the average refractive index of the optical fiber core, c is the speed of light in vacuum, and Lall is the length of the single-mode passive optical fiber (3).

4. The ultrafast fiber laser according to claim 3, characterized in that , the value of T6 is less than 1ns, the pulse cluster repetition frequency f r Greater than 1GHz.

5. The ultrafast fiber laser according to claim 1, characterized in that The adjustable optical delay line (4) includes an input portion (41), a reflection portion (42), an adjustable range (43) and an output portion (44); The reflecting portion (42) and the adjustable range (43) are fixedly connected, and the output portion (44) is driven to move laterally by the translation of the adjustable range (43). In addition, the input portion (41), the output portion (44) and the two reflecting surfaces of the reflecting portion (42) are designed in a coordinated manner so that the input light and the output light are continuously in a parallel relationship during the translation process.

6. The ultrafast fiber laser according to claim 5, characterized in that The adjustable range (43) is manually rotated to move horizontally, thereby driving the output portion (44) to move horizontally together, or the adjustable range (43) is controlled to move horizontally by an electric control fine adjustment mechanism, thereby driving the output portion (44) to move horizontally together.

7. The ultrafast fiber laser according to claim 5, characterized in that ,In the initial adjustment, the adjustable optical delay line (4) is controlled to be in the middle position of the ,adjustable range (43).

8. The ultrafast fiber laser according to claim 3, wherein: The synchronous repetition frequency signal output by the seed source (1) is transmitted to the control module (12) through its own SMA adapter. The control module (12) controls the first acousto-optic modulator (10) and the second acousto-optic modulator (11) to generate a modulation signal synchronized with the seed source (1) with a fixed time delay T2. The repetition frequency of the modulation signal and the duty cycle within one cycle are determined according to the following relationship: T3+T4 is the length of one cycle of the first acousto-optic modulator (10), T3 is the length of the high level cycle of the first acousto-optic modulator (10), indicating the length of time the delay loop is open within a single first acousto-optic modulator (10) modulation cycle, T3 is N times the length of the ultrafast seed source cycle T, used to control the maximum number of pulses in the pulse cluster of the delay superposition cycle in the loop, the number of pulses superimposed in the maximum pulse cluster is N, T4 is used to end the pulse superposition cycle in the loop within a single first acousto-optic modulator (10) modulation cycle, T4 is M times the length of the ultrafast seed source cycle T, wherein in order to achieve an effective cycle cut-off function, the value of M must be greater than 1. After this condition is met, after the modulation signal of the single first acousto-optic modulator (10) starts, the number of pulses superimposed in the loop will increase from 1 to N again, and cycle in this way, that is, the length of one first acousto-optic modulator (10) modulation signal cycle is (N+M)*T in total, and the corresponding repetition frequency is 1 / ((N+M)*T).

9. The ultrafast fiber laser according to claim 7, wherein: The function of the second acousto-optic modulator (11) is to select and output a desired superimposed pulse cluster, and the fixed time delay between the rising edge of its modulation signal and the signal of the first acousto-optic modulator (10) is T5, and the adjustment range of T5 is (0, (N-1)*T); The high level time in a single cycle of the second acousto-optic modulator (11) is T1, that is, the pulse period of a single ultrafast seed source, thereby selecting a desired pulse cluster and suppressing an undesired pulse cluster.

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