Fiber laser with wave packet pulse train output based on pulse-pumped passive Q-switching technology

Abstract

This invention discloses a fiber laser that achieves wave packet pulse train output based on pulse-pumped passive modulation technology. The device includes a pump source; a (2+1)×1 combiner; rare-earth-doped double-clad gain fiber; a passively Q-switched material; a flange; a high-reflectivity fiber Bragg grating; a low-reflectivity fiber Bragg grating; and a function generator. A TTL modulation signal is selected and input to the pump source to obtain wave packet pulses. By changing the modulation frequency of the signal, the number of sub-pulses within the wave packet is changed, thus providing a fiber laser solution that allows adjustment of the number of sub-pulses within the wave packet pulse train as needed.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic technology, and more specifically, to a novel method for generating wave packet pulse train output in a fiber laser using pulse pump passive modulation technology. Background Technology

[0002] Compared to single-pulse lasers, pulse train lasers possess the characteristics of high repetition rate, narrow pulse width, high peak power, and high pulse energy, thus holding significant application value and research significance in fields such as precision machining, optical diagnostic imaging, nonlinear frequency conversion, human tissue ablation, and lithotripsy. Pulse trains include square-wave pulse trains and wave packet pulse trains. A square-wave pulse train refers to a pulse train with a square-wave envelope, while a wave packet pulse train has a Gaussian or Lorentzian envelope. In particular, wave packet pulse trains (also known as superpulses) in the 2-micron wavelength band have important applications in human tissue ablation and lithotripsy. Currently, methods for generating wave packet pulse trains in fiber lasers include increasing pump power, positive dispersive harmonic mode-locking, pulse multipliers, self-Q-switching mode-locking, increasing cavity nonlinearity and net anomalous dispersion, high-reflectivity coupled output mirrors, self-phase modulation, and weak saturated absorption. However, once the experimental setup is fixed, the number of pulses within the output wave packet pulse train cannot be changed using these methods. Therefore, there is an urgent need for a fiber laser solution that allows for adjustment of the number of pulses within a wave packet pulse train as needed. In view of this, an apparatus and method are provided for externally adjusting the number of output pulses in a wave packet pulse train of a fiber laser. Summary of the Invention

[0003] This invention, based on the adjustable frequency, pump time, and pump power of the pump signal in pulse pumping technology, and combined with passive Q-switching technology, proposes a pulse pumping passive modulation technique. Furthermore, based on the structure of fiber lasers, a fiber laser that utilizes pulse pumping passive modulation technology to achieve wave packet pulse train output is ultimately proposed. The device includes: Pump source: The pump source in a fiber laser is a semiconductor laser (LD). The output wavelength of the fiber pump source, which serves as the pump gain, must match the absorption wavelength required for population inversion of the laser wavelength that generates the wave packet pulse train. Arbitrary function signal generator: used to control the frequency, period, and pulse shape of the time-domain pulse signal output by the pump source; High-reflectivity fiber Bragg grating mirror: The high-reflectivity fiber Bragg grating mirror is based on the principle of light interference and is fabricated using the phase mask method and ultraviolet exposure. The light-inlet end face of this device is cut at an 8-degree angle.

[0004] The beam combiner is a (2+1)×1 type. There are two inlet fiber channels for the pump light and one fiber channel for the wavepack laser. The pump light fiber is located on both sides, with the wavepack laser fiber in the middle. This fiber is connected to the output end of the high-reflectivity fiber grating mirror via fusion splice. On the other side of the beam combiner is another wavepack laser fiber, which is connected to one end of the gain fiber via fusion splice.

[0005] Gain fiber: Gain fiber is a rare-earth ion-doped fiber, using 10 / 130mm double-clad fiber, to improve pump efficiency. One end of the fiber is connected to a combiner via fusion splicing, and the other end is made with an FC / APC connector.

[0006] Low-reflectivity fiber Bragg grating mirror: The fabrication method for low-reflectivity fiber Bragg grating mirrors is the same as that for high-reflectivity fiber Bragg grating mirrors. The input end face of this device is an FC / APC connector, and the output end face is cut at an 8-degree angle.

[0007] Passive Q-switching materials: Passive Q-switching materials are two-dimensional crystal materials, such as MoS2 and MoSe2. These materials are flexible and not easily broken.

[0008] Flange: It is used not only to connect the light inlet of the gain fiber and the low reflectivity fiber grating mirror, but also to place the two-dimensional passive Q-switching material between the end faces of the two fibers.

[0009] By utilizing an arbitrary function signal generator, the frequency and power of the pump pulse signal are made dually adjustable, thereby controlling the periodicity of the population inversion distribution and achieving discontinuous passive Q-switched continuous pulses. With a constant pump power, the number of sub-pulses within an output pulse train can be significantly altered by changing the frequency of the pump pulse signal. This method allows for the easy generation of pulse train lasers with an adjustable number of sub-pulses, and it has significant applications in precision machining, optical diagnostic imaging, human tissue ablation, and lithotripsy. Attached Figure Description

[0010] Figure 1 Optical path diagram of an embodiment disclosed in this invention Figure 2 Wave packet pulse time-domain pulse sequence diagram Detailed Implementation

[0011] To further clarify the advantages of the proposed solution, detailed descriptions are provided below with reference to embodiments. All technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0012] It should be noted that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well, and the use of terms such as "passive Q-switching material" in this application refers to specific features and structural characteristics described in connection with the embodiment being included in one embodiment of the application. The illustrative expressions of the above terms do not necessarily refer to the same embodiment. Moreover, different two-dimensional passive Q-switching materials, by replacing a specific material, constitute a specific embodiment. Furthermore, those skilled in the art can replace the different examples described in this specification with other Q-switching materials.

[0013] As described in the background art, the inventors obtained wave packet pulse train output based on changes in the optical resonator structure, and the number of sub-pulses within a pulse train cannot be changed, which greatly limits the clinical medical effects of human tissue ablation and lithotripsy. In order to generate wave packet pulse train laser with adjustable sub-pulse number, this application proposes a device and method for realizing the output wave packet pulse train of fiber laser using pulse pump passive modulation technology. Example

[0014] In a typical embodiment of this application, the optical path diagram of the entire device is as follows: Figure 1 As shown. Figure 1 In the diagram, there are: 1. Arbitrary signal function generator; 2. Pump source; 3. High reflectivity fiber grating mirror; 4. Combiner; 5. Thulium-doped silica fiber; 6. Flange; 7. Fiber grating mirror with low reflectivity at 1940nm.

[0015] Arbitrary signal function generator 1 is used to debug the time-domain sequence of pump light pulses required for the output of the pump source. Pump source 2 is a semiconductor laser diode with an output wavelength of 793nm, using a 105 / 125 fiber to output pump light. Under the adjustment of an arbitrary function signal generator, it outputs pump light pulse time-domain sequences of different waveforms and frequencies. The output power of the pump light is not controlled by the signal generator but is supplied solely by the pump source's power supply.

[0016] The high-reflectivity fiber grating reflector 3 has a reflectivity of over 99% for the laser center wavelength of 1940nm.

[0017] The combiner 4 is a (2+1)×1 fiber combiner. One end (input end) has three fiber channels. The middle one is the channel for the pulsed laser, specifically the 1940nm laser, and is made of 10 / 125 silica fiber. It connects to the high-emissivity fiber grating reflector 3. The two outer fibers are the pump light channels. The upper fiber connects to the output fiber of pump source 2, and the lower fiber can also connect to the output fiber of pump source 2. The other end of the combiner has one fiber channel connected to the thulium-doped silica fiber 5 (gain fiber).

[0018] Thulium-doped silica fiber 5. Thulium-doped silica fiber is a silica fiber with a core diameter of 10 mm and a cladding diameter of 125 mm. It achieves population inversion by absorbing 793 nm pump light and generates laser light through stimulated emission.

[0019] Flange 6 is used to house the passive Q-switching material, connect the gain fiber, and link the low-reflectivity fiber grating mirror. The passive Q-switching material is a thin film formed by compressing two-dimensional molybdenum disulfide nanomaterials, with a thickness of 36 mm, a modulation depth of 24.64%, and a saturation energy flux density of 156.75 mJ / cm². 2 The unsaturated absorption is 69.29%, and it is placed between the gain fiber and the low reflectivity fiber grating mirror to generate Q-switched pulsed lasers.

[0020] The low-reflectivity fiber grating reflector 7 has a reflectivity of 10% for light with a wavelength of 1064nm, and together with the high-reflectivity fiber grating reflector 3, they form an optical resonant cavity. Specific implementation methods

[0021] according to Figure 1 The fiber supplying the pump source output light is fused with the incident fiber of one channel of the pump light at the combiner input end using a fusion splicer. The fiber supplying the pulse train laser channel at the combiner input end is fused with a high-reflectivity fiber grating mirror. The fiber supplying the combiner output end is fused with a thulium-doped gain fiber. An FC / APC connector is fabricated at the other end of the gain fiber. An FC / APC connector is also fabricated at the input end of the low-reflectivity mirror fiber. The FC / APC connector of the gain fiber is first connected via a flange, then molybdenum disulfide two-dimensional nanomaterial is placed inside the flange, and finally the FC / APC connector of the low-reflectivity mirror fiber is connected. The power switch of the pump source is turned on, and the current is gradually increased. The output spot is observed using an infrared card. Then, the infrared card is removed, and a high-speed pulse detector is installed. The output pulse waveform is observed on an oscilloscope to confirm that the entire laser system is operating normally. Finally, the function generator is connected to the pump source. The pump source current is fixed, and the TTL waveform of the signal generator is selected to obtain the following results: Figure 2The image shows a wave packet pulse train laser. Changing the modulation frequency of the signal changes the number of pulse trains. Example

[0022] The optical path in this embodiment is the same as in Embodiment 1, except that the molybdenum disulfide two-dimensional nanomaterial is replaced with molybdenum ditelluride two-dimensional nanomaterial. The obtained wave packet pulse diagram is... Figure 1 Similarly, only the pulse width of the wave packet pulse, the number of sub-pulses within the wave packet, and the pulse width of the sub-pulses are slightly different. When the modulation frequency is changed, the change pattern of the number of pulse trains is the same as in Example 1.

[0023] This embodiment discloses a fiber laser that uses pulse-pumped passive modulation technology to achieve wave packet pulse train output. This laser has important application value in clinical medicine fields such as human tissue ablation and lithotripsy.

[0024] The above description is merely an embodiment of this application and is not intended to limit this application. For those skilled in the art, this application can be applied to obtain wave packet pulse trains in different bands. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A fiber laser for realizing wave-packet pulse train output based on a pulse-pumped passive modulation technique, characterized in that, The fiber laser that achieves wave packet pulse train output based on pulse-pumped passive modulation technology includes: Gain fiber, one end of which is made with an FC / APC connector, allows the passive Q-switching material to be placed at an angle; The low-reflectivity fiber grating mirror has an FC / APC connector on the light-inlet end face, which facilitates the tilting of the passive Q-switching material and its close connection with the gain fiber, while also fixing the passive Q-switching material. A flange is an integrated device that combines connection and placement. It consists of one end of a gain fiber with an end face made of an FC / APC connector, passive Q-switching material, and low-reflectivity fiber, and the light-inlet end of a grating mirror is tightly connected together. The function signal generator is used to generate TTL pulse electrical signals, which in turn generate pulse pump optical signals, causing the number inversion of particles in the gain fiber to change periodically, resulting in the output of wave packet pulse trains; by changing the modulation frequency of the TTL pulse electrical signals, the number of sub-pulses within the wave packet pulses can be changed.

2. The fiber laser for wave packet pulse train output based on pulse-pumped passive modulation technology as described in claim 1, characterized in that, The passively Q-switched material is placed at an angle.

3. The fiber laser for wave packet pulse train output based on pulse-pumped passive modulation technology as described in claim 1, characterized in that, One end of the gain fiber is made into the end face of an FC / APC connector, so that the passive Q-switching material is in complete contact with the gain fiber.

4. The fiber laser for wave packet pulse train output based on pulse-pumped passive modulation technology as described in claim 1, characterized in that, The end face of the light-inlet end of the low-reflectivity fiber grating mirror is made into an FC / APC connector to fix the passive Q-switching material.

5. The fiber laser for wave packet pulse train output based on pulse-pumped passive modulation technology as described in claim 1, characterized in that, Use a flange to tightly connect the FC / APC connector end face of the gain fiber, the FC / APC connector end face of the light inlet of the low reflectivity fiber grating mirror, and the passive Q-switching material.

6. The fiber laser for wave packet pulse train output based on pulse-pumped passive modulation technology as described in claim 1, characterized in that, By changing the modulation frequency of the function signal generator to control the pulse frequency of the pump light, the number of sub-pulses within the output laser wave packet pulse light can be controlled without changing the structure of the laser system.

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