A PytBu saturable absorber device and an erbium-doped mode-locked fiber laser device

Abstract

The present invention belongs to the technical field of passively mode-locked ultrafast fiber lasers, and discloses a PytBu saturable absorber device and an erbium-doped mode-locked fiber laser device. The PytBu saturable absorber device is prepared by mixing PytBu saturable absorber particles and absolute ethanol, ultrasonically dispersing the mixture, centrifuging the mixed solution, taking the upper layer of the PytBu saturable absorber particle dispersion after centrifugation, coating it on the surface of a D-type or tapered fiber, and drying it in a vacuum-sealed manner, so that the PytBu saturable absorber particles cover the surface of the D-type or tapered fiber. The ultrashort pulse sequence of the PytBu saturable absorber device of the present invention is uniform and has stable performance. The structure of the erbium-doped mode-locked laser device based on the PytBu saturable absorber device is simple and compact, adopting an all-fiber structure, with high beam quality, good stability, convenient fusion splicing and easy maintenance. Mode-locked pulse output is achieved by adjusting the pump energy and the polarization controller.

Description

Technical Field

[0001] The present invention belongs to the technical field of pulsed fiber lasers, and more specifically, relates to a PytBu saturable absorber device and an erbium-doped mode-locked fiber laser device. Background Art

[0002] In fiber lasers, the optical fiber serves as a waveguide medium. With a relatively small core diameter, a high power density is easily formed inside the fiber core. The fiber has excellent flexibility, enabling the structure of the fiber laser to be designed to be very compact, with a small volume and easy system integration. In addition, fiber lasers also have advantages such as being free from adjustment, maintenance-free, high stability, and high conversion efficiency. Therefore, fiber lasers have good application potential in fields such as scientific research, precision machining and manufacturing, medical treatment, communication, aerospace, etc. As an important branch of fiber lasers, pulsed fiber lasers can achieve the adjustment of dispersion and fiber nonlinearity by adjusting the cavity length of the laser, etc., to achieve pulsed outputs with different performances, and are important potential scientific research products with very broad applications.

[0003] In pulsed fiber lasers, using a saturable absorber (SA) to achieve Q-switching or mode-locked pulse output is the most commonly used and simplest technical means. The saturable absorber has a saturation effect on the absorption of light, specifically manifested as the absorption ability of light decreasing with the increase of light intensity, which is a material with optical nonlinear characteristics. The basic mechanism of saturable absorber mode-locking is that when a light pulse passes through the absorber, the loss of the part with lower power is greater than that of the part with lower power, so that only the part with higher power of the light pulse can pass through. As a result, the light pulse is narrowed during the process of passing through the saturable absorber. In order to obtain high-performance pulsed lasers, researchers have studied various saturable absorbers to achieve Q-switching and mode-locked pulsed lasers. Currently, saturable absorbers are mainly divided into two categories: artificial saturable absorbers and real saturable absorbers. As a typical real saturable absorber, semiconductor saturable absorber mirrors (SESAMs) are widely used in mode-locked lasers. The parameters of SESAMs can be artificially regulated, so people can fabricate specific SESAMs according to actual needs to achieve the desired effects. However, the preparation process of SESAMs is complex and the cost is high, which severely restricts their application fields. Therefore, finding real saturable absorber materials with better performance and lower cost is an urgent need at present.

[0004] In recent years, materials such as graphene, carbon nanotubes (CNTs), black phosphorus (BP), topological insulators (TIs), transition metal dichalcogenides (TMDs), oxides, Mxenes, and organic semiconductors have received extensive attention from researchers. In recent years, organic π-conjugated luminescent molecules have shown great application potential in organic electronics, nonlinear optics, energy storage devices, and biological probes. Among them, organic fluorophores with fluorescence quenching properties have advantages such as long excitation wavelengths and small photobleaching. In addition, the conjugated structure in organic small molecules leads to a relatively weak binding force of organic small molecules to valence electrons, resulting in the splitting of energy levels. This structure has a significant modulation effect on the optical nonlinearity of materials. In 2020, researchers reported the application of an 8-hydroxyquinoline aluminum salt (Alq3), a luminescent material for OLEDs, as a saturable absorber in ultrafast lasers (IET Optoelectronics, 2020.14(5): p. 234-241.). Therefore, as a luminescent organic small molecule semiconductor material with aggregation-induced fluorescence quenching properties, it is also a potential new type of saturable absorber material. Summary of the Invention

[0005] To address the above-mentioned deficiencies and drawbacks of the prior art, the primary objective of the present invention is to provide a PytBu saturable absorber device, which uses the luminescent organic small molecule 8-[4-(2-methylpropan-2-yl)phenyl]-1,3,6-tris-{[2-methylpropan-2-yl)phenyl]ethynyl}pyrene[2,1-b]furan (abbreviated as PytBu) with aggregation-induced fluorescence quenching properties as the saturable absorber, and the PytBu saturable absorber particles are covered on the surface of a D-type or tapered optical fiber.

[0006] Another objective of the present invention is to provide a mode-locked fiber laser device based on the above PytBu saturable absorber device.

[0007] The objectives of the present invention are achieved through the following technical solutions:

[0008] A PytBu saturable absorber device, in which the PytBu saturable absorber device is prepared by mixing PytBu saturable absorber particles with aggregation-induced fluorescence quenching properties and absolute ethanol, ultrasonically dispersing the mixture, centrifuging the mixed solution, and coating the upper-layer PytBu saturable absorber particle dispersion after centrifugation on the surface of a D-type or tapered optical fiber, and then drying it in a vacuum-sealed environment so that the PytBu saturable absorber particles cover the surface of the D-type or tapered optical fiber.

[0009] Preferably, the mass ratio of the PytBu saturable absorber particles to the volume of absolute ethanol is (1-2) mg: 200 mL, and the particle size of the PytBu saturable absorber particles is 5-10 μm.

[0010] Preferably, the time of ultrasonic dispersion is 24-48 h, the centrifugation speed is 3000-5000 rpm, and the centrifugation time is 3-5 min.

[0011] An erbium-doped mode-locked fiber laser device, which includes a laser pump source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, an output coupler, a polarization controller, the PytBu saturable absorber device, and a single-mode fiber connected in sequence.

[0012] Further, the wavelength division multiplexer includes a first output end, a second output end, and an input end; the output coupler includes a 90% output end, a 10% output end, and an input end; the laser pump source is connected to the input end of the wavelength division multiplexer, and the PytBu saturable absorber device is connected to the second output end of the wavelength division multiplexer through a single-mode fiber to form a ring resonator; the polarization-independent isolator is connected to the 90% output end of the output coupler; the input end of the output coupler is connected to the polarization controller.

[0013] Preferably, the gain fiber is an erbium-doped fiber with a length of 100-120 cm, the wavelength of the laser pump source is 974-978 nm, and the central wavelength of the wavelength division multiplexer is 1545-1565 nm.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The present invention uses the luminescent organic small molecule PytBu with aggregation fluorescence quenching as a saturable absorber to generate pulsed light in the near-infrared band. The ultrashort pulse sequence based on the PytBu saturable absorber is uniform and has stable performance, is easy to achieve mode locking, generates ultrashort pulse laser, and expands the application of the luminescent organic small molecule PytBu in the field of laser mode-locking broadband absorption.

[0016] 2. The tapered fiber of the present invention can further increase the damage threshold of the longer nonlinear interaction length between light and the PytBu saturable absorber, and flexibly control the thickness and length of the tapered region of the tapered fiber to adjust the performance of the saturable absorber device.

[0017] 3. The mode-locked pulse laser device based on the PytBu saturable absorber device of the present invention has a simple and compact structure, is easy to operate, adopts an all-fiber structure, has high beam quality, good stability, is convenient for fusion splicing and coupling, and is easy to maintain. The mode-locked pulse output is achieved by adjusting the pump energy with a polarization controller.

[0018] 4. The preparation method of the PytBu saturable absorber device of the present invention is simple and can be realized for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the molecular formula of the organic molecule of PytBu in Example 1.

[0020] Figure 2 is a schematic diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1.

[0021] Figure 3 is the pulse sequence diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw.

[0022] Figure 4 is the spectrogram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw.

[0023] Figure 5 is the autocorrelation trace and fitting curve diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw.

[0024] Figure 6 is the radio frequency diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw.

[0025] Figure 7 is the relationship diagram of different pump powers and corresponding output powers of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 in the mode-locked state. DETAILED DESCRIPTION OF THE INVENTION

[0026] The content of the present invention will be further described below in conjunction with specific embodiments, but it should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise stated, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0027] Example 1

[0028] 1. Put 10 mg of PytBu saturable absorber particles (the molecular formula is as Figure 1The obtained supernatant is the PytBu saturable absorber particle dispersion, wherein the particle size of the PytBu particles is 5 to 10 μm.

[0029] 2. Coat the dispersion of PytBu saturable absorber particles on the surface of D-type or tapered optical fiber, dry it naturally in a vacuum-sealed container, and cover the surface of D-type or tapered optical fiber with PytBu saturable absorber particles to obtain a PytBu saturable absorber device.

[0030] Example 2

[0031] 1. Add 10 mg of PytBu saturable absorber particles (molecular formula Figure 1 The obtained supernatant is a PytBu saturable absorber and particle dispersion, wherein the particle size of the PytBu saturable absorber particles after dispersion is 5 to 10 μm.

[0032] 2. Coat the dispersion of PytBu saturable absorber particles on the surface of D-type or tapered optical fiber, dry naturally in a vacuum-sealed container, and cover the surface of D-type or tapered optical fiber with PytBu saturable absorber particles to obtain a PytBu saturable absorber device.

[0033] Application Example 1

[0034] Figure 2 This is a schematic diagram of a mode-locked fiber laser device based on a PytBu saturable absorber device in Application Example 1. 1 is a laser pump source, 2 is a wavelength division multiplexer, 3 is an erbium-doped fiber, 4 is a polarization-independent isolator, 5 is an output coupler, 6 is a polarization controller, 7 is a PytBu saturable absorber device, and 8 is a single-mode fiber. 21 is the first output end of the wavelength division multiplexer, 22 is the second output end of the wavelength division multiplexer, 23 is the input end of the wavelength division multiplexer, 51 is the 90% output end of the output coupler, 52 is the 10% output end of the output coupler, and 53 is the input end of the output coupler.

[0035] A mode-locked fiber laser device with a ring structure is fabricated by using a laser pump source 1 (with a wavelength of 976 nm), a wavelength division multiplexer 2, an erbium-doped fiber 3, a polarization-independent isolator 4, an output coupler 5 (with a 90:10 coupling ratio, which divides a laser beam into two laser beams, and the power ratio of these two beams is 90:10, that is, 10% is output and 90% continues to circulate in the optical path), a polarization controller 6 (using a three-piece coil rotation type), a PytBu saturable absorber device 7 prepared in Example 1, and a single-mode fiber 8. The ring cavity length is 9 m.

[0036] The wavelength division multiplexer 2 includes a first output end 21, a second output end 22, and an input end 23; the output coupler 5 includes a 90% output end 51, a 10% output end 52, and an input end 53; the output end of the laser pump source 1 is connected to the input end 23 of the wavelength division multiplexer 2 by an optical fiber fusion splicer, the first output end 21 of the wavelength division multiplexer 2, the erbium-doped fiber 3, the polarization-independent isolator 4, and the 90% output end 51 of the output coupler 5 are connected, the input end 53 of the output coupler 5, the polarization controller 6, the PytBu saturable absorber device 7, the single-mode fiber 8, and the second output end 22 of the wavelength division multiplexer 2 are connected in sequence. Both ends of the PytBu saturable absorber device 7 are connected to the second output end 22 of the wavelength division multiplexer 2 and the polarization controller 6 respectively by a single-mode fiber 8. Instruments such as an oscilloscope, an autocorrelator, a spectrometer, and a power meter are connected to the 10% output port 52 of the output coupler 5 to measure the laser output characteristics of the mode-locked fiber laser.

[0037] Figure 3 This is the pulse sequence diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw. From Figure 3 it can be seen that the mode-locked pulses in the cavity of the mode-locked fiber laser device work in a relatively stable state, the pulse interval is 46.26 ns, and the corresponding pulse repetition frequency is 21.62 MHz. Figure 4 This is the spectrogram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw. From Figure 4 it can be seen that the full width at half maximum of the spectrum is 6.24 nm, and the central wavelength is 1568.36 nm. Figure 5 This is the autocorrelation trace and fitting curve diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw. From Figure 5 it can be seen that the pulse width is 720 fs. Figure 6 This is the radio frequency diagram of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 under a pump power of 90 mw. Among them, (a) is the pulse signal-to-noise ratio at a repetition frequency of 21.62 MHz. (b) is the pulse signal-to-noise ratio in the range from 0 GHz to 1 GHz. From Figure 6It can be seen that the signal-to-noise ratio of the pulse is 60.5 dB, indicating that the pulse signal is very stable. Figure 7 It is a relationship diagram of different pump powers and corresponding output powers of the mode-locked fiber laser device based on the PytBu saturable absorber device in Application Example 1 in the mode-locked state. From Figure 7 It can be seen that as the pump power increases, the pulse output power also gradually increases, and the two are roughly linearly related. To sum up, the mode-locked pulse fiber laser device provided by the present invention has a pulse repetition frequency of 21.62 MHz, a pulse width of 720 fs, a pulse signal-to-noise ratio that can reach 60.5 dB, and good pulse stability.

[0038] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A PytBu saturable absorber device, characterized in that, The PytBu saturable absorber device is prepared by mixing PytBu saturable absorber particles with aggregation fluorescence quenching property and absolute ethanol, ultrasonically dispersing the mixture, centrifuging the mixed solution, taking the upper layer of the PytBu saturable absorber particle dispersion after centrifugation and coating it on the surface of a D-type or tapered optical fiber, and drying it in a vacuum tight manner so that the PytBu saturable absorber particles cover the surface of the D-type or tapered optical fiber.

2. The PytBu saturable absorber device according to claim 1, characterized in that, The mass ratio of the PytBu saturable absorber particles to the volume of absolute ethanol is (1 - 2) mg: 200 mL, and the particle size of the PytBu saturable absorber particles is 5 - 10 μm.

3. The PytBu saturable absorber device according to claim 1, wherein The time for the ultrasonic dispersion is 24 - 48 h, the rotation speed for the centrifugation is 3000 - 5000 rpm, and the time for the centrifugation is 3 - 5 min.

4. An erbium-doped mode-locked fiber laser device, characterized in that, The erbium-doped mode-locked fiber laser device includes a laser pump source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, an output coupler, a polarization controller, the PytBu saturable absorber device according to any one of claims 1 - 3, and a single-mode fiber, which are connected in sequence.

5. The erbium-doped mode-locked fiber laser device according to claim 4, characterized in that, The wavelength division multiplexer includes a first output end, a second output end, and an input end; the output coupler includes a 90% output end, a 10% output end, and an input end; the laser pump source is connected to the input end of the wavelength division multiplexer, the PytBu saturable absorber device is connected to the second output end of the wavelength division multiplexer through a single-mode fiber to form a ring resonator; the polarization-independent isolator is connected to the 90% output end of the output coupler; the input end of the output coupler is connected to the polarization controller.

6. The erbium-doped mode-locked fiber laser device according to claim 4 or 5, characterized in that The gain fiber is an erbium-doped fiber with a length of 100 - 120 cm, the wavelength of the laser pump source is 974 - 978 nm, and the central wavelength of the wavelength division multiplexer is 1545 - 1565 nm.

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