Saturable absorber device, method of manufacture and low threshold start-pulse mode-locked laser

Abstract

The application provides a saturable absorption device, a preparation method and a low-threshold starting pulse mode-locked laser, and relates to the technical field of lasers. The application discloses a method for preparing a high-quality bismuth copper selenium oxide single crystal by a chemical vapor transport method, and a saturable absorption device prepared by simply using the high-quality bismuth copper selenium oxide single crystal can be applied to a pulse mode-locked laser, and can generate super-short pulse laser output, has high stability and a high signal-to-noise ratio, and has a low starting threshold.

Description

Saturable absorber device, fabrication method and low threshold start-up pulse mode-locked laser Technical Field

[0001] This invention mainly relates to the field of optical device and laser design technology, and in particular to a saturable absorber device, its fabrication method, and a low threshold start-up pulse mode-locked laser. Background Technology

[0002] This research aims to develop novel ultrashort pulse lasers based on two-dimensional material saturable absorbers, overcoming the reliance on semiconductor saturable absorber mirrors in traditional passive mode-locked pulsed laser technology and the problems of complex structure, unstable operation, and limited bandwidth associated with traditional saturable absorbers. It also addresses the challenges faced by existing two-dimensional material mode-locked pulsed lasers, such as coupling efficiency, stability, and noise. This will facilitate the realization of compact, low-start-threshold, high-power pulsed lasers.

[0003] In passive mode-locking technology, saturable absorbers are widely used in various ultrafast lasers due to their simple structure and stable performance. However, limited by semiconductor materials and device structures, the operating bandwidth of semiconductor absorbers is typically below 100 nanometers, making them unsuitable for applications such as ultrawideband tunable and mid-infrared pulsed lasers. Novel two-dimensional materials possess excellent nonlinear optical effects, strong light-matter interactions, and ultrawide operating bandwidths, effectively compensating for the shortcomings of silicon-based semiconductor materials. Considered ideal materials for saturable absorption, they have attracted the attention of numerous researchers and provided new ideas for the development of traditional ultrafast photonics and breakthroughs in device performance.

[0004] Current pulsed lasers based on low-dimensional two-dimensional saturable absorber materials mostly rely on methods such as tape or ionic solution thinning to obtain ultrathin materials. This inevitably introduces defects, adhesive residue, and impurities, leading to fiber contamination. Impurities and defective nanomaterials can cause insertion loss and reflection, causing light energy to concentrate at impurity sites or propagate backward. These factors suppress light transmission and can damage transceivers. This is common in cavities without isolators (to isolate backward-propagating light). Furthermore, due to experimental practices, tight alignment during patch cord or pigtail connections allows dust, adhesive residue, or crystal debris to easily transfer from one fiber end face to the other, significantly limiting the start-up threshold during pulse formation.

[0005] Bismuth-copper-selenium-oxygen nanocrystals exhibit many interesting properties, showing superior nonlinear absorption with varying ionic element content. However, their applications in ultrafast photonics have not yet been reported. Summary of the Invention

[0006] In view of the limitations of existing technologies in the directional growth of materials such as bismuth, copper, selenium, and oxygen, the relatively complex fabrication of saturable absorber devices based on two-dimensional materials, and the high start-up threshold (hundreds of milliwatts) of pulsed mode-locked lasers based on two-dimensional materials, this invention proposes a saturable absorber device, a fabrication method, and a low-threshold start-up pulsed mode-locked laser.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for fabricating a saturable absorber device, comprising:

[0009] (1) Prepare materials according to the weight parts, and place the mixed source, which is composed of 10 parts of bismuth trioxide powder, 1 part of copper powder and some KCl powder, into a tube furnace;

[0010] (2) Place the freshly cleaved mica substrate directly above the hybrid source to enable the growth of bismuth copper selenide oxygen nanosheets;

[0011] (3) Take another 5 portions of bismuth triselenide and place them in the high-temperature section of the tubular furnace upstream of the mixing source and at a certain distance from the mixing source;

[0012] (4) Heat the high-temperature section of the tubular furnace to a temperature that allows bismuth triselenide to volatilize and decompose, hold for several minutes, and then cool down to room temperature with the furnace.

[0013] (5) Remove the mica substrate and the bismuth copper selenide nanosheets grown on the mica substrate.

[0014] (6) Transfer the bismuth copper selenide oxygen nanosheets grown on the mica substrate to the end face of the single-mode fiber jumper and align them with the core position of the end face of the single-mode fiber jumper to complete the fabrication of the saturable absorber device.

[0015] Furthermore, step (5) also includes: performing X-ray diffraction characterization on the bismuth copper selenide oxygen nanosheets grown on the mica substrate. Sharp, periodic X-ray diffraction peaks indicate that the grown bismuth copper selenide oxygen nanosheets are high-quality single crystals and exhibit signal peaks at the (012) contact crystal plane. Saturable absorber devices made with high-quality bismuth copper selenide oxygen single crystals will have superior optical properties.

[0016] Furthermore, in step (4), the high-temperature section of the tubular furnace is heated to 650℃-670℃.

[0017] Furthermore, in step (4), maintain for 5-10 minutes.

[0018] Furthermore, in step (3), the other 5 portions of bismuth triselenide are placed 5cm to 15cm away from the mixing source.

[0019] Furthermore, in step (6), the bismuth copper selenide oxygen nanosheets grown on the mica substrate are transferred to the end face of the single-mode fiber jumper by the method of optical fiber electrostatic adsorption.

[0020] On the other hand, the present invention provides a saturable absorption device, which is manufactured using the above-described method for preparing a saturable absorption device.

[0021] On the other hand, the present invention provides a low threshold start-up pulse mode-locked laser, including a ring cavity, wherein a saturable absorber fabricated using the above-described method for fabricating saturable absorbers is connected in the ring cavity.

[0022] Compared with the prior art, the technical effects of the present invention are as follows:

[0023] This invention provides a method for fabricating a saturable absorber device, which can directionally grow high-quality bismuth-copper-selenium-oxygen single crystals.

[0024] This invention provides a simple way to fabricate saturable absorption devices from high-quality bismuth copper selenide oxygen single crystals, which have superior optical properties.

[0025] The saturable absorber device made by this invention can be applied to pulsed mode-locked lasers to generate pulsed lasers with low start-up threshold and ultra-short pulse width. Attached Figure Description

[0026] 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 the structures shown in these drawings without creative effort.

[0027] Figure 1 is a schematic diagram showing the positional relationship of various materials in a tube furnace during the fabrication of a saturable absorber device according to an embodiment.

[0028] Figure 2 is an optical image of bismuth copper selenide nanosheets grown on a mica substrate obtained in one embodiment;

[0029] Figure 3 is an X-ray diffraction characterization diagram of bismuth copper selenide oxygen nanosheets grown on mica substrate in one embodiment of the present invention.

[0030] Figure 4 is a schematic diagram of the preparation of a saturable absorber device using bismuth copper selenide oxygen nanosheets in one embodiment, where (a) is the initial preparation state, (b) is the transfer of bismuth copper selenide oxygen nanosheets grown on the mica substrate by means of optical fiber electrostatic adsorption, (c) is the placement of bismuth copper selenide oxygen nanosheets aligned with the core position of the end face of a single-mode optical fiber jumper, and (d) the prepared saturable absorber device is obtained.

[0031] Figure 5 shows the nonlinear absorption and Fourier transform infrared absorption spectroscopy results of a saturable absorber device prepared in one embodiment, where (a) is the result of nonlinear absorption test of the prepared saturable absorber device, and (b) is the result of Fourier transform infrared absorption spectroscopy test of the prepared saturable absorber device.

[0032] Figure 6 is a schematic diagram of a low-threshold start-up pulse mode-locked laser provided in one embodiment;

[0033] Figure 7 shows the experimental results of a low-threshold start-up pulsed mode-locked laser provided in an embodiment, where (a) is a pulse sequence diagram under the start-up threshold pump power; (b) is a fundamental frequency signal diagram; (c) is a wide-range spectrum signal diagram; (d) is a spectrum center wavelength diagram of the pulsed laser output by the low-threshold start-up pulsed mode-locked laser in this embodiment; and (e) is a pulse width diagram of the pulsed laser output by the low-threshold start-up pulsed mode-locked laser in this embodiment. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the disclosed content will be clearly explained below with reference to the accompanying drawings and detailed description. Any person skilled in the art, after understanding the embodiments of the present invention, can make changes and modifications based on the techniques taught in the present invention without departing from the spirit and scope of the present invention. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0035] In one embodiment, a method for fabricating a saturable absorber is provided, comprising:

[0036] (1) Prepare materials according to the weight parts, and place the mixed source, which is composed of 10 parts of bismuth trioxide powder, 1 part of copper powder and some KCl powder, into a tube furnace;

[0037] (2) Place the freshly cleaved mica substrate directly above the hybrid source to enable the growth of bismuth copper selenide oxygen nanosheets;

[0038] (3) Take another 5 portions of bismuth triselenide and place them in the high-temperature section of the tubular furnace upstream of the mixing source and at a certain distance from the mixing source;

[0039] (4) The high-temperature section of the tube furnace is heated to a temperature that allows bismuth triselenide to volatilize and decompose, held for several minutes, and then cooled to room temperature with the furnace. This high-temperature heating step will cause bismuth triselenide to volatilize and decompose, producing Bi and Se atoms in the target product. Finally, by naturally cooling to room temperature, bismuth copper selenide oxygen nanosheets can be obtained on the mica substrate.

[0040] (5) Remove the mica substrate and the bismuth copper selenide nanosheets grown on the mica substrate.

[0041] (6) Transfer the bismuth copper selenide oxygen nanosheets grown on the mica substrate to the end face of a single-mode fiber optic patch cord (the specific model is not limited, such as the SMF 28e model) and align it with the core position of the end face of the single-mode fiber optic patch cord to complete the fabrication of the saturable absorber device.

[0042] Furthermore, step (5) also includes: performing X-ray diffraction characterization on the bismuth copper selenide oxygen nanosheets grown on the mica substrate. Sharp, periodic X-ray diffraction peaks indicate that the grown bismuth copper selenide oxygen nanosheets are high-quality single crystals and exhibit signal peaks at the (012) contact crystal plane. Saturable absorber devices made with high-quality bismuth copper selenide oxygen single crystals will have superior optical properties.

[0043] In addition, X-ray diffraction tests revealed that the bismuth copper selenide oxide nanosheets grown on the mica substrate in the oblique growth mode have one more crystal plane (012) than those in the planar growth mode. This creates a prerequisite for probe-assisted transfer (pure dry transfer technology) and ensures that damage and chemical residues are minimized during the transfer process.

[0044] Furthermore, in one embodiment, it is proposed that in step (6), the bismuth copper selenide oxygen nanosheets grown on the mica substrate are transferred to the end face of the single-mode fiber jumper by means of optical fiber electrostatic adsorption.

[0045] Furthermore, in one embodiment, it is proposed that in step (3), the additional 5 portions of bismuth triselenide are placed at a distance of 5 cm to 15 cm from the mixing source.

[0046] In one embodiment, a method for fabricating a saturable absorber is provided, comprising:

[0047] (1) A mixed source consisting of 0.5g bismuth trioxide powder, 0.05g copper powder and a certain amount of KCl powder is placed in a tube furnace;

[0048] (2) Freshly cleaved fluorine crystal mica substrate (chemical formula: KMg3(AlSi3O) 10 F2) is placed directly above the hybrid source to enable the growth of bismuth copper selenide oxygen nanosheets;

[0049] (3) Take another 0.25g of bismuth triselenide and place it in the high-temperature section of the tube furnace, which is about 10cm upstream of the mixing source and about 10cm away from the mixing source. The positional relationship of the mixing source, the fluorine mica substrate and the newly taken bismuth triselenide in the tube furnace is shown in Figure 1. In Figure 1, A represents the mixing source; B represents the fluorine mica substrate; and C represents the newly taken 0.25g of bismuth triselenide.

[0050] (4) Heat the high-temperature section of the tube furnace to a temperature of 650℃-670℃, which is sufficient to volatilize and decompose bismuth triselenide, and hold for several minutes (e.g., 5-10 minutes), then allow the furnace to cool naturally to room temperature. This high-temperature heating step will cause bismuth triselenide to volatilize and decompose, producing Bi and Se atoms in the target product. Finally, by allowing it to cool naturally to room temperature, bismuth copper selenide oxygen nanosheets can be obtained on the fluorinated mica substrate, as shown in Figure 2.

[0051] (5) The fluorinated mica substrate and the bismuth copper selenide nanosheets grown on the fluorinated mica substrate were removed. X-ray diffraction characterization was performed on the bismuth copper selenide nanosheets grown on the mica substrate to confirm that the obtained bismuth copper selenide nanosheets were high-quality single crystals. Specifically, sharp, periodic X-ray diffraction peaks indicated that the grown bismuth copper selenide nanosheets were high-quality single crystals.

[0052] (6) Transfer the high-quality single-crystal bismuth copper selenide oxygen nanosheets grown on the fluorine-crystal mica substrate to the end face of a single-mode fiber optic patch cord (the specific model is not limited, such as SMF 28e model) and align it with the core position of the end face of the single-mode fiber optic patch cord to complete the fabrication of the saturable absorber device, as shown in Figure 4. (a) is the initial preparation state, (b) is the transfer of the bismuth copper selenide oxygen nanosheets grown on the mica substrate by the fiber electrostatic adsorption method, (c) is the placement of the bismuth copper selenide oxygen nanosheets aligned with the core position of the end face of the single-mode fiber optic patch cord, and (d) the prepared saturable absorber device is obtained.

[0053] The fabricated saturable absorber was subjected to nonlinear absorption and Fourier transform infrared (FTIR) absorption spectroscopy tests. The test results are shown in Figure 5, where (a) is the result of the nonlinear absorption test of the fabricated saturable absorber, and (b) is the result of the Fourier transform infrared (FTIR) absorption spectroscopy test of the fabricated saturable absorber. As shown in Figure 5, it exhibits stable absorption in the near-infrared band. The modulation depth of the fabricated saturable absorber is approximately 36%, and the saturation power is approximately 24 kW / cm². 2 .

[0054] This invention prepares highly oriented oblique bismuth copper selenide oxygen nanosheets via chemical vapor transport. Benefiting from the oblique orientation, these nanosheets facilitate the simple fabrication of bismuth copper selenide oxygen fiber-based saturable absorber devices.

[0055] On the other hand, the present invention provides a saturable absorption device, which is manufactured using the saturable absorption device preparation method provided in any of the above embodiments.

[0056] On the other hand, the present invention provides a low threshold start-up pulse mode-locked laser, including a ring cavity, wherein a saturable absorber fabricated using the above-described method for fabricating saturable absorbers is connected in the ring cavity.

[0057] As shown in Figure 6, a low threshold start-up pulse mode-locked laser provided in one embodiment of the present invention includes a ring cavity, specifically a ring formed by sequentially connecting a wavelength division multiplexer 1, an erbium-doped gain fiber 3, a polarization-independent isolator 4, a polarization controller 5, a saturable absorber 6, and a coupler 7, wherein a laser diode 2 is connected to the other access arm of the wavelength division multiplexer 1.

[0058] In one embodiment, a low-threshold start-up pulse mode-locked laser is provided, employing the ring cavity shown in Figure 6. This ring cavity includes a 2.2m erbium-doped gain fiber and a 12.8m single-mode fiber. With appropriate polarization control, the laser can output stable mode-locked pulses at pump powers ranging from ~30 to 830mW, as shown in Figure 7. Figure 7(a) shows the pulse sequence at the start-up threshold pump power, with a detected pulse separation of 66.7ns. Figures 7(b) and (c) show the spectral signal, with a high fundamental frequency signal-to-noise ratio and an intensity of approximately 61 dB. Figure 7(d) shows its soliton-like pulse spectrum. As shown in Figure 7(e), the mode-locked laser of this embodiment can generate pulsed laser output with a pulse width of 395 fs.

[0059] In summary, pulsed mode-locked lasers based on bismuth-copper-selenium-oxygen saturable absorber devices can generate ultrashort pulse laser outputs with high stability and signal-to-noise ratio, especially with a low start-up threshold.

[0060] Matters not covered in this invention are common knowledge.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for fabricating a saturable absorber, characterized in that, include: (1) Prepare materials according to the weight parts, and place the mixed source, which is composed of 10 parts of bismuth trioxide powder, 1 part of copper powder and some KCl powder, in a tube furnace; (2) Place the freshly cleaved mica substrate directly above the mixed source to achieve the growth of bismuth copper selenide nanosheets; (3) Take another 5 parts of bismuth triselenide and place them upstream of the mixed source and at a certain distance from the mixed source in the high-temperature section of the tube furnace; (4) Heat the high-temperature section of the tube furnace to a temperature that allows bismuth triselenide to volatilize and decompose, maintain it for several minutes, and then cool it down to room temperature with the furnace; (5) Take out the mica substrate and the bismuth copper selenide nanosheets grown on the mica substrate; (6) Transfer the bismuth copper selenide nanosheets grown on the mica substrate to the end face of the single-mode fiber jumper and align it with the fiber core position of the end face of the single-mode fiber jumper to complete the fabrication of the saturable absorber device.

2. The method for fabricating a saturable absorber according to claim 1, characterized in that, Step (5) further includes: performing X-ray diffraction characterization on bismuth copper selenide oxygen nanosheets grown on a mica substrate. Sharp, periodic X-ray diffraction peaks indicate that the grown bismuth copper selenide oxygen nanosheets are high-quality single crystals.

3. The method for fabricating a saturable absorber according to claim 1, characterized in that, In step (4), the high-temperature section of the tubular furnace is heated to 650℃-670℃.

4. The method for fabricating a saturable absorber according to claim 1, characterized in that, In step (4), maintain for 5-10 minutes.

5. The method for fabricating a saturable absorber according to claim 1, 2, 3, or 4, characterized in that, In step (3), the other 5 portions of bismuth triselenide are placed 5cm to 15cm away from the mixing source.

6. The method for fabricating a saturable absorber according to claim 5, characterized in that, The mica substrate is a fluorine-crystalline mica substrate.

7. The method for fabricating a saturable absorber according to claim 1, characterized in that, In step (6), bismuth copper selenide oxygen nanosheets grown on a mica substrate are transferred to the end face of a single-mode fiber jumper using an optical fiber electrostatic adsorption method.

8. A saturable absorption device, characterized in that, It is manufactured using the saturable absorber fabrication method as described in claim 1, 2, 3, 4, 6, or 7.

9. The saturable absorption device according to claim 8, characterized in that, The saturable absorber has a modulation depth of 36% and a saturation power of 24 kW / cm². 2 .

10. A low-threshold start-up pulse mode-locked laser, comprising a ring cavity, characterized in that, The saturable absorber device, prepared using the method described in claim 1, 2, 3, 4, 6, or 7, is connected in the annular cavity.

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