Array carbon nanotube film saturable absorber, preparation method and laser

Abstract

The invention provides an array carbon nanotube film saturable absorber, a preparation method and a laser, and the preparation method comprises the steps: dissolving carbon nanotube powder and a high-molecular polymer in a toluene solution to obtain a mixed solution, carrying out the ultrasonic treatment of the mixed solution, and carrying out the centrifugal treatment of the mixed solution after the ultrasonic treatment; depositing the centrifuged mixed solution on the surface of a substrate to form an array carbon nanotube film; spin-coating two organic compound layers on one surface of the substrate on which the array carbon nanotube film is deposited; fixing the substrate spin-coated with the organic compound above the transfer solution, heating the transfer solution, and stripping the array carbon nanotube film from the organic compound layer; and transferring the stripped array carbon nanotube film and the organic compound layer to the end surface of the optical fiber, and removing the organic compound layer from the end surface of the optical fiber after natural air drying for a preset time. According to the invention, the modulation depth of the saturable absorber of the fiber laser is improved, and the manufacturing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to an array of carbon nanotube thin film saturable absorbers, their preparation method, and a laser. Background Technology

[0002] With the rapid development of laser technology, ultrafast mode-locked fiber lasers have been able to generate femtosecond-level ultrashort pulses, which have significant application value in ultrafast imaging, optical communication, spectral analysis, biomedicine, and materials processing. Compared with traditional solid-state lasers, fiber lasers have advantages such as high beam quality, high efficiency, compact structure, and good stability. The emergence of wavelength-tunable mode-locked pulsed lasers has further expanded the application range of lasers. Doped fibers of different elements can provide effective gains in different wavelength bands, corresponding to different laser output wavelength ranges. Among them, erbium-doped fiber lasers have an output range of C / C+L band, covering the communication window around 1550nm, and have high application value in communication systems. Narrow pulse width femtosecond lasers have become a key indicator for optimizing mode-locked lasers, and can be used to compress the detection time window to the actual time scale of physical, chemical, or biological processes (such as molecular vibration, charge transfer, chemical reactions, etc.), for ultrafast pump-probe experiments and transient absorption spectroscopy.

[0003] However, existing mode-locked lasers struggle to meet both performance requirements simultaneously, and their performance remains limited, particularly in terms of material selection and system performance. For example, traditional SESAMs (saturable absorber mirrors) require specific wavelength design, resulting in high manufacturing costs and limited bandwidth. Therefore, improving the modulation depth of the saturable absorber in mode-locked fiber lasers and reducing their manufacturing costs are pressing technical challenges. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide an arrayed carbon nanotube thin film saturable absorber, a preparation method, and a laser to eliminate or improve one or more defects existing in the prior art.

[0005] In one aspect, the present invention provides a method for preparing an arrayed carbon nanotube thin film saturable absorber, the method comprising: Carbon nanotube powder and polymer were dissolved in toluene solution to obtain a mixed solution. The mixed solution was then ultrasonically treated, and the ultrasonically treated mixed solution was centrifuged. The centrifuged mixed solution was deposited on the surface of a substrate to form an array of carbon nanotube films by solution deposition. Two layers of organic compounds were spin-coated on one of the surfaces of the substrate with the deposited array of carbon nanotube films. A transfer solution is prepared using hydrofluoric acid and water. A substrate with an organic compound spin-coated on it is fixed above the transfer solution. The transfer solution is then heated to peel off the arrayed carbon nanotube film and the organic compound layer from the substrate. The arrayed carbon nanotube film and the organic compound layer obtained by stripping are transferred to the end face of an optical fiber. After a period of natural wind intervention, the organic compound layer is removed from the end face of the optical fiber to obtain an arrayed carbon nanotube film saturable absorber.

[0006] In some embodiments of the present invention, removing the organic compound layer from the end face of the optical fiber to obtain an arrayed carbon nanotube thin film saturable absorber includes: The end face of the optical fiber containing the arrayed carbon nanotube film and the organic compound layer is fixed above the acetone solution; Heating the acetone solution removes the organic compound layer on the end face of the optical fiber; The end face of the optical fiber with the organic compound layer removed is air-dried to obtain an array of carbon nanotube thin film saturable absorber.

[0007] In some embodiments of the present invention, two organic compound layers are spin-coated onto one surface of a substrate on which an array of carbon nanotube films are deposited, including: The substrate with the deposited array of carbon nanotube films was vacuum adsorbed onto a spin coater; An organic compound solution is dropped onto one of the surfaces of the substrate and left to stand for a preset time. Start the spin coater and spin-coat the polyimide solution evenly onto the corresponding surface.

[0008] In some embodiments of the present invention, the ratio of hydrofluoric acid to water in the transfer solution is 1:18 to 1:22; and / or, The spin coater rotates at 1500 revolutions per second and the spin coater rotates for one minute.

[0009] In some embodiments of the present invention, the arrayed carbon nanotube film is formed by multiple single carbon nanotubes arranged in parallel and spaced intervals.

[0010] According to another aspect of the present invention, an arrayed carbon nanotube thin film saturable absorber is also provided, which is prepared by the preparation method of the arrayed carbon nanotube thin film saturable absorber as described in any of the above embodiments.

[0011] According to another aspect of the present invention, a hybrid mode-locked laser is also disclosed, the hybrid mode-locked laser comprising: a pump source, a wavelength division multiplexer, a coupler, an erbium-doped fiber, a polarization controller module, and an arrayed carbon nanotube thin film saturable absorber as described in the above embodiments; The output of the pump source is connected to the input of the wavelength division multiplexer. The signal light output of the wavelength division multiplexer is connected to the input of the arrayed carbon nanotube thin film saturable absorber. The output of the arrayed carbon nanotube thin film saturable absorber is connected to the input of the coupler. The output of the coupler is connected to the input of the polarization controller module. The output of the polarization controller module is connected to the first end of the erbium-doped fiber. The second end of the erbium-doped fiber is connected to the pump light output of the wavelength division multiplexer.

[0012] In some embodiments of the present invention, the polarization controller module includes a first polarization controller, a polarization-dependent polarizer, and a second polarization controller. The input terminal of the first polarization controller is connected to the output terminal of the coupler, and the output terminal of the second polarization controller is connected to the first end of the erbium-doped fiber. The polarization-dependent polarizer is located between the output terminal of the first polarization controller and the input terminal of the second polarization controller. The first polarization controller is used to adjust the polarization state, and the second polarization controller is used to adjust the birefringence phase.

[0013] In some embodiments of the present invention, the hybrid mode-locked laser further includes a dispersion compensation module located between the polarization controller module and the erbium-doped fiber.

[0014] In some embodiments of the present invention, the dispersion compensation module includes an SMF-28 optical fiber, and the length of the SMF-28 optical fiber ranges from 1.3m to 1.8m.

[0015] The arrayed carbon nanotube thin film saturable absorber prepared by the above-described embodiments of the present invention achieves excellent photoelectric performance through its unique structural design. It can cover a broad C / C+L spectral range around 1550 nm, effectively absorbing light within this range. Simultaneously, it exhibits good nonlinear effects, improving the tunable range of NPR mode-locking and significantly enhancing the material's wavelength tuning capability. During the preparation of the saturable absorber, a dry transfer method was employed, successfully achieving a balance between modulation depth and damage threshold, significantly improving the material's performance and stability, and meeting the requirements of high-efficiency lasers. Therefore, the arrayed carbon nanotube thin film saturable absorber of this application not only improves modulation depth but also reduces its manufacturing cost. In addition to the above, this application combines arrayed carbon nanotube thin film saturable absorbers with the nonlinear polarization rotation effect in optical fibers to construct a novel hybrid mode-locked fiber laser. This hybrid mode-locked cavity combines the advantages of real and artificial saturable absorption mechanisms, which can not only further compress the pulse width but also achieve dynamic wavelength tuning. Specifically, placing a real SA module in the hybrid mode-locked laser achieves wavelength tunability, generating mature femtosecond pulse output with wavelength tuning capability and excellent stability. This application optimizes the performance of carbon nanotubes, simplifies the laser structure, reduces system complexity, and achieves synergistic operation of wide wavelength tuning and ultrashort pulse width.

[0016] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the description, or may be learned by practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures specifically pointed out in the description and drawings.

[0017] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. The components in the drawings are not drawn to scale but are merely illustrative of the principles of the invention. For ease of illustration and description of certain parts of the invention, corresponding portions in the drawings may be enlarged, i.e., may appear larger relative to other components in an exemplary device actually manufactured according to the invention. In the drawings: Figure 1 This is a schematic flowchart illustrating a method for preparing an arrayed carbon nanotube thin film saturable absorber according to an embodiment of this application.

[0019] Figure 2This is a schematic diagram of the structure of an arrayed carbon nanotube thin film saturable absorber according to an embodiment of this application.

[0020] Figure 3 This is a schematic diagram of the architecture of a hybrid mode-locked laser according to an embodiment of this application.

[0021] Figure 4 This is a spectrum of different wavelengths of a hybrid mode-locked laser according to an embodiment of this application.

[0022] Figure label: Pump source 100, wavelength division multiplexer 200, arrayed carbon nanotube thin film saturable absorber 300, coupler 400, first polarization controller 510, polarization-dependent polarizer 520, second polarization controller 530, erbium-doped fiber 600, oscilloscope 700, arrayed carbon nanotube thin film 310 Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0024] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0025] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0026] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection with an intermediary, and can refer not only to a wired connection, but also to a wireless connection. The specific meaning can be changed based on the actual application scenario.

[0027] Traditional SESAMs (Semiconductor Saturable Absorber Mirrors) sometimes employ two-dimensional materials like graphene or topological insulators to achieve broadband bandwidth, but achieving both modulation depth and damage threshold is difficult, often resulting in trade-offs. Carbon nanotubes (CNTs), due to their unique one-dimensional structure and band structure, are excellent saturable absorbers; single-walled CNTs can be viewed as rolled-up graphene sheets, thus possessing discrete band structures and van Hoff singularities, with their band gap and absorption wavelength determined by the tube diameter and chirality. Currently, while random CNT films in the 1.0–1.6 μm range have been successfully applied, randomly oriented films suffer from limitations in polarization control and modulation controllability. Their nonlinear parameters (such as modulation depth and saturation intensity) are significantly affected by the fabrication process, making repeatability and consistency difficult to guarantee. Therefore, this invention provides a method for fabricating arrayed CNT thin film saturable absorbers, enabling tunability of the saturable absorber in mode-locked fiber lasers and reducing the manufacturing cost of mode-locked fiber lasers.

[0028] In addition to the above, traditional pure NPR mode-locked lasers are limited in pulse width, with pulse widths in the picosecond range, failing to meet femtosecond requirements and thus limiting their application scenarios. Furthermore, the wavelength tuning mechanisms of existing pure NPR mode-locked lasers are relatively complex, typically requiring external filters and other discrete components, increasing system complexity and cost. Additionally, the wavelength tuning capability of existing pure NPR mode-locked lasers is limited. Many applications, such as different channels in optical communication, different absorption lines in optical sensing, and spectral research, require tunable center wavelengths of the mode-locked source. However, a fixed-configuration fiber laser typically operates only near the gain peak of the gain medium (e.g., erbium-doped fiber typically operates in the 1530–1565 nm C-band). Traditionally, achieving tunability requires the introduction of tunable filters, grating pairs, and other components, which undoubtedly increase system complexity. Moreover, the insufficient operating bandwidth of the saturable absorber (SA) in existing mode-locked fiber lasers limits their tunable range.

[0029] In summary, existing saturable absorbers and mode-locked fiber lasers suffer from drawbacks such as non-tunability and high manufacturing costs. Therefore, this invention provides an arrayed carbon nanotube thin film saturable absorber, its preparation method, and a laser, which, while ensuring the performance of fiber lasers, improves the modulation depth of the saturable absorber in mode-locked fiber lasers, reduces manufacturing costs, and enables the simple integration of tunable, femtosecond-level narrow pulse width systems.

[0030] The one-dimensional quantum structure of carbon nanotubes endows them with remarkable nonlinear optical properties, including ultrafast carrier response and wide-band saturable absorption. Compared to traditional semiconductor saturable absorber mirrors (SESAMs), carbon nanotube SAs offer significant advantages such as fast recovery time, low saturation intensity, polarization insensitivity, large modulation depth, wide operating bandwidth, good environmental stability, and low fabrication cost. These properties make carbon nanotube SAs a highly promising component in mode-locked fiber lasers and have successfully driven the development of ultrafast fiber lasers. The inventors discovered in their research that randomly distributed CNT networks often produce uncontrollable local concentration and orientation differences during fabrication, resulting in significant dispersion of parameters (modulation depth, loss, threshold) of different batches of saturable absorbers, making it difficult to repeat the output characteristics of the laser. Arrayed CNTs, due to their ordered macroscopic structure, have uniform and controllable density and orientation of nanotubes in each device, thus achieving better batch-to-batch performance repeatability. In other words, the disordered structure of traditional disordered CNT films, characterized by "fiber entanglement," significantly affects the optical properties of the device and makes it difficult to reproduce the output mode of ultrashort pulse lasers. This application solves these problems in the prior art by using an ordered nanotube structure.

[0031] Furthermore, existing lasers typically require discrete components such as external filters for wavelength tuning, increasing system complexity and cost. This application addresses this by designing an all-fiber laser structure that integrates a dispersion management module with NPR-SA hybrid mode-locking technology, thereby simplifying the system architecture, reducing reliance on external components, and improving system reliability and ease of use. Moreover, existing mode-locked lasers struggle to achieve a balance between wavelength tuning and ultrashort pulse widths (<500 fs); this application designs a novel system architecture that ensures the laser can achieve a wider wavelength tuning range without sacrificing pulse width.

[0032] In the following description, embodiments of the invention will be illustrated with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar parts, or the same or similar steps.

[0033] First, the present invention provides a method for preparing an arrayed carbon nanotube thin film saturable absorber, that is, by growing and assembling carbon nanotube thin films in an array, a high-quality, high-density arrayed carbon nanotube thin film saturable absorber is obtained, which has the characteristics of high modulation depth and strong nonlinear absorption effect. Figure 1 This is a schematic flowchart of a method for preparing an arrayed carbon nanotube thin film saturable absorber according to an embodiment of the present invention, as shown below. Figure 1 As shown, the preparation method includes at least steps S10 to S40.

[0034] Step S10: Dissolve carbon nanotube powder and polymer in toluene solution to obtain a mixed solution, sonicate the mixed solution using an ultrasonic machine, and centrifuge the sonicated mixed solution using a centrifuge.

[0035] Step S20: The centrifuged mixed solution is deposited on the surface of the substrate to form an array of carbon nanotube films by solution deposition. Two organic compound layers are spin-coated on one of the surfaces of the substrate with the deposited array of carbon nanotube films.

[0036] Step S30: Prepare a transfer solution based on hydrofluoric acid and water, fix the substrate with the organic compound spin-coated on it above the transfer solution, heat the transfer solution, and peel the arrayed carbon nanotube film and the organic compound layer off the substrate.

[0037] Step S40: Transfer the obtained arrayed carbon nanotube film and the organic compound layer to the end face of an optical fiber. After a period of natural wind intervention, remove the organic compound layer from the end face of the optical fiber to obtain an arrayed carbon nanotube film saturable absorber.

[0038] To address the limitations of traditional mode-locked lasers, such as narrow wavelength tuning range and restricted pulse width, the above-mentioned fabrication method utilizes arrayed carbon nanotube (CNT) bandgap engineering to prepare a saturable absorber. Specifically, the substrate can be either a silicon substrate or a silicon dioxide substrate. The process involves first preparing a carbon nanotube solution, then depositing an arrayed carbon nanotube film on a Si / SiO2 substrate using solution deposition, and finally transferring the arrayed carbon nanotube film to the fiber end face using a dry transfer process to create the saturable absorber.

[0039] For example, removing the organic compound layer from the end face of the optical fiber to obtain a saturable absorber of an arrayed carbon nanotube film may specifically include the following steps: fixing the end face of the optical fiber containing the arrayed carbon nanotube film and the organic compound layer above an acetone solution; heating the acetone solution to remove the organic compound layer from the end face of the optical fiber; and air-drying the end face of the optical fiber with the organic compound layer removed to obtain a saturable absorber of an arrayed carbon nanotube film.

[0040] Furthermore, two organic compound layers are spin-coated onto one surface of a substrate with a deposited array of carbon nanotube films. Specifically, this may include: vacuum-adsorbing the substrate with the deposited array of carbon nanotube films onto a spin coater; dropping an organic compound solution onto one surface of the substrate and allowing it to stand for a preset time; starting the spin coater and uniformly spin-coating the polyimide solution onto the corresponding surface. The spin coater's rotation speed can be set to 1500 revolutions per second, and the spin coater's rotation time is one minute.

[0041] In one specific embodiment, the arrayed carbon nanotube film can be prepared according to the following steps: 1. Dissolve carbon nanotube powder and polymer PCz in toluene solution to obtain a mixed solution; 2. Sonicate the mixed solution in a low-temperature water bath for 30 minutes using an ultrasonicator; 3. Centrifuge for 3 hours using a high-speed centrifuge to remove impurities; 4. Deposit the arrayed carbon nanotube film on the surface of a Si / SiO2 substrate using solution deposition. After the arrayed carbon nanotube film is prepared, it can be further transferred to the end face of an optical fiber using a dry transfer method to prepare an arrayed carbon nanotube saturable absorber.

[0042] Furthermore, the specific preparation method of the arrayed carbon nanotube thin film saturable absorber can be carried out using the following steps: 1. Spin-coating two layers of copolymer (organic compound) onto the surface of a Si / SiO2 substrate sample with deposited arrayed carbon nanotube thin film; 2. Preparing a transfer solution by mixing HF acid and water at a ratio of 1:20; 3. Fixing the substrate sample with the spin-coated layer above the transfer solution; 4. Heating the transfer solution to complete the peeling of the arrayed carbon nanotube thin film and the spin-coated layer; 5. Transferring the peeled arrayed carbon nanotube thin film and the spin-coated layer to the end face of an optical fiber and air-drying for 24 hours; 6. Preparing an acetone solution; 7. Fixing the structure prepared in step 5 above the acetone solution; 8. Heating the acetone to remove the spin-coated layer of the structure from step 5; 9. Air-drying the structure from step 8 for 24 hours to obtain the arrayed carbon nanotube thin film saturable absorber. In this embodiment, the ratio of HF acid (hydrofluoric acid) to water in the transfer solution is 1:20. It is understood that this ratio is only an example, and other ratios are also possible, such as 1:18 to 1:22.

[0043] Furthermore, it is understandable that the aforementioned arrayed carbon nanotube film 310 is composed of multiple single carbon nanotubes arranged in parallel and spaced intervals (e.g., Figure 2 (As shown) To evaluate the properties of the arrayed carbon nanotube thin film saturable absorber 300 prepared by the above preparation method, the linear transmission spectrum and nonlinear saturable absorption characteristics of the CNT-SA film were further tested. The test results showed that the absorption rate of the film exceeded 80% in the wavelength range of 1000 nm to 1650 nm. This ultra-high broadband absorption characteristic is attributed to the combined absorption effect of different chiral carbon nanotubes, indicating that the SA can cover a wide spectral range of 1 µm to 1.6 µm, and the corresponding laser can achieve wide-range tuning.

[0044] In addition, to evaluate the nonlinear absorption characteristics of the arrayed CNTs (also known as arrayed carbon nanotube thin film saturable absorbers 300), a P-scan testing system was built to test arrayed CNTs with different numbers of layers. The results show that the prepared arrayed CNTs exhibit excellent nonlinear absorption capabilities and show significant modulation depth during pulse compression and wavelength tuning. This makes the arrayed CNTs an ideal choice for achieving efficient pulse compression and wavelength tuning, providing strong material support for the high-performance operation of lasers.

[0045] Furthermore, this invention also discloses a hybrid mode-locked laser, which achieves coordinated control of the array CNT band engineering and hybrid mode-locking mechanism through coordinated optimization. This not only improves the tuning performance of the laser, but also ensures the stability and efficiency of the pulse output.

[0046] like Figure 3 As shown, the hybrid mode-locked laser may specifically include a pump source 100, a wavelength division multiplexer 200, a coupler 400, an erbium-doped fiber 600, a polarization controller module, and an array of carbon nanotube thin film saturable absorbers 300 prepared based on the preparation method of any of the above embodiments.

[0047] The output of pump source 100 is connected to the input of wavelength division multiplexer 200. The signal light output of wavelength division multiplexer 200 is connected to the input of arrayed carbon nanotube thin film saturable absorber 300. The output of arrayed carbon nanotube thin film saturable absorber 300 is connected to the input of coupler 400. The output of coupler 400 is connected to the input of polarization controller module. The output of polarization controller module is connected to the first end of erbium-doped fiber 600. The second end of erbium-doped fiber 600 is connected to the pump light output of wavelength division multiplexer 200.

[0048] In the above embodiments, the hybrid mode-locked laser includes several key modules, such as a gain module, a saturable absorber module, and a polarization control module. These key modules work together to achieve wide wavelength tuning and femtosecond-level pulse compression. The gain module uses erbium-doped fiber (EDF) as the gain medium and is pumped by a 980 nm semiconductor laser (Innolume GmbH) with a maximum power of 1000 mW. The pump power is monitored and adjusted in real time by computer software to ensure the stability of the laser and the constant output power. The polarization control module is used to adjust the polarization state and birefringence phase within the cavity, thereby achieving mode-locking adjustment and wavelength range tunability. By adjusting the polarization control module, the polarization state within the cavity can be precisely controlled, achieving wide wavelength tuning of the laser. In terms of pulse generation and shaping, the saturable absorber plays a crucial role as the SA module. This module integrates an array of CNT thin films onto the fiber end face and connects to the cavity via an FC / PC fiber connector. It not only effectively adjusts the pulse width but also coordinates the control of wavelength tuning, further optimizing the laser output characteristics.

[0049] In the above embodiment, the 1550 nm laser diode can be forward-pumped with an erbium-doped fiber (3 m) via a 980 nm / 1550 nm wavelength division multiplexer (WDM) 200, and the unidirectional propagation of light is ensured by a polarization-independent isolator (ISO). The polarization state within the cavity is adjusted by a polarization controller, and the output signal is directed to an oscilloscope 700 for monitoring via a coupler 400. A single-mode fiber (SMF) is introduced into the cavity to optimize pulse quality, and pulse generation and shaping are achieved in conjunction with an array of carbon nanotube thin film saturable absorbers 300. Finally, the center wavelength is optimized by adjusting the PC module (polarization controller module) to further improve mode-locking characteristics and ensure the efficient and stable operation of the laser. Specifically, the polarization controller module may include a first polarization controller 510 (PC1) and a second polarization controller 530 (PC2).

[0050] In one embodiment, the polarization controller module includes a first polarization controller 510, a polarization-dependent polarizer 520, and a second polarization controller 530. The input terminal of the first polarization controller 510 is connected to the output terminal of the coupler 400, and the output terminal of the second polarization controller 530 is connected to the first end of the erbium-doped fiber 600. The polarization-dependent polarizer 520 is located between the output terminal of the first polarization controller 510 and the input terminal of the second polarization controller 530. The first polarization controller 510 is used to adjust the polarization state, and the second polarization controller 530 is used to adjust the birefringence phase.

[0051] Specifically, in Figure 3In the hybrid mode-locked laser shown, the high-power 980nm pump light output from the pump source 100 is sent to the wavelength division multiplexer 200. The wavelength division multiplexer 200 separates the pump light from the 1550nm signal light inside the cavity through wavelength selective beam splitting and directionally injects the pump light into an erbium-doped fiber to excite erbium ions and generate gain amplification. Simultaneously, the signal light is sent to a saturable absorber, which compresses the pulse width to the femtosecond level through nonlinear absorption characteristics and filters the optical signal with a specific polarization state. The optical signal then enters the first polarization controller 510 and the second polarization controller 530. The first polarization controller 510 and the second polarization controller 530 work together to adjust the polarization state and birefringence phase of the light inside the cavity, optimizing the nonlinear polarization rotation mode-locking effect and ensuring pulse stability. At the same time, the polarization-dependent polarizer 520 filters and locks the optical signal with the target polarization direction, suppressing noise interference. The shaped optical signal is split proportionally by coupler 400: 20% is sent to oscilloscope 700 to monitor the pulse time-domain characteristics (pulse width, repetition frequency) and spectral morphology in real time, and 80% is fed back to wavelength division multiplexer 200 to form a closed loop and continue to participate in the operation.

[0052] The hybrid mode-locked laser of the above embodiments of the present invention achieves coordinated operation of each module by combining passive mode-locking, NPR active tuning, and a hybrid mode-locking mechanism, thereby optimizing the performance of the fiber laser. Specifically, arrayed carbon nanotube nonlinear absorption is used to achieve pulse narrowing, effectively compressing the pulse width through a passive mode-locking mechanism. Other commonly used tuning methods (such as resonant cavities composed of bulk optical devices such as dichroic mirrors and lens groups) have not achieved all-fiber operation, which not only greatly limits the structural compactness and operational reliability of fiber lasers, but also increases the difficulty of pump light coupling, and is not conducive to the matching and compatibility between fiber lasers and subsequent fiber optic systems. This application uses NPR tuning to achieve tunability of the center wavelength. This tuning method can greatly simplify the tuning system, eliminate the need to introduce other additional optical components, greatly increase system integration, and simplify the wavelength tuning process. Furthermore, the tuning method used in the laser of this application achieves continuous tuning of the wavelength around 1550nm. In addition to the above, dynamic dispersion management utilizes a combination of SMF (single-mode fiber) and EDF (erbium-doped fiber) to optimize near-zero dispersion transmission, further improving system stability and transmission efficiency.

[0053] In the hybrid mode-locked laser of the above embodiment, the collaborative working mechanism achieves laser stability and high-performance output by precisely controlling the parameters of each module. First, during mode-locking triggering and pulse generation, the initial condition is set to a pump power of 80mW (threshold). PC2 is adjusted to the critical mode-locking state, and pulse formation is observed using an oscilloscope at 700°. After observation, the pump power is further increased. At this point, the nonlinear absorption effect of the CNT array further compresses the pulse width, enabling the output pulse to reach the femtosecond level, thereby improving the laser's temporal resolution. Next, in the wavelength tuning operation, coarse tuning is first performed by rotating PC1 to adjust the polarization state and monitoring the wavelength shift on the spectrometer in real time to complete the initial wavelength tuning. Then, fine tuning is performed by finely adjusting the pump power and PC2, utilizing the self-phase modulation (SPM) effect to expand the spectral bandwidth, thereby precisely controlling the wavelength tuning process and optimizing the wavelength output.

[0054] In some embodiments of the present invention, the hybrid mode-locked laser further includes a dispersion compensation module located between the polarization controller module and the erbium-doped fiber 600. In this embodiment, a dispersion compensation method is used to compress the pulse width and optimize the pulse quality for pulse compression optimization. For example, the dispersion compensation module includes an SMF-28 fiber, and the length of the SMF-28 fiber ranges from 1.3m to 1.8m; specifically, a 1.5m SMF-28 fiber can be introduced to compress the pulse width.

[0055] After pulse compression, the above embodiments used LabVIEW to monitor system stability in real time. After an 8-hour stability test, the results showed that the center wavelength drift was less than 0.3 nm and the power fluctuation standard deviation was less than 1.5%, ensuring the stability and reliability of the laser during long-term operation. Therefore, based on the optimization of the saturable absorber and laser structure, this application effectively solves the problems of wide pulse width and inconvenient tuning in traditional mode-locked lasers, promoting the application of ultrashort pulse lasers in precision manufacturing, bioimaging, and other fields.

[0056] Figure 4 In the image, (a), (b), (c), and (d) are the spectra with center wavelengths of 1559 nm, 1562.3 nm, 1564.6 nm, and 1566.5 nm, respectively. Figure 4As shown, the laser disclosed in this application is continuously tuned from 1559 nm to 1566.5 nm, achieving a tuning range of 7.5 nm. The laser in this application achieves wavelength tunability by adjusting the angle of the polarization controller. Compared to current methods that add filters within the cavity to achieve wavelength tunability, the laser in this application only requires adjusting the polarization control (PC). Continuous wavelength tunability is achieved through the birefringence filtering effect of the PC and PS-ISO. The device structure is simple and stable, and it has a wider tuning range than graphene materials.

[0057] Furthermore, the laser of this application can achieve femtosecond-level ultrashort pulse output; that is, by utilizing the unique design of the arrayed CNT material, the pulse width is successfully compressed to 237 fs, close to the theoretical transformation limit, and the time-bandwidth product is 0.318, close to the theoretical limit of 0.315. The unique arrangement mechanism of the array gives it a higher nonlinear absorption coefficient than single-walled carbon nanotubes and other disordered-grown CNT materials at the same light intensity, thereby improving the modulation depth of passive mode-locking; the high modulation depth directly reduces the mode-locking threshold and accelerates the pulse narrowing process.

[0058] In addition to the above, the laser of this application also exhibits high power stability and high integration; specifically, after 8 hours of continuous operation, the center wavelength drift of the laser is less than 0.3 nm, and the standard deviation of power fluctuation is less than 1.5%, demonstrating its excellent stability and reliability. Furthermore, the laser's damage threshold reaches 3.5 GW / cm², far exceeding the 1.5 GW / cm² of traditional saturable absorbers (SAs), ensuring stable operation under high power output and meeting the requirements of high-power laser applications. The hybrid mode-locked structure used simultaneously significantly reduces system complexity, providing excellent conditions for all-fiber integration.

[0059] As can be seen from the above embodiments, this application employs an arrayed carbon nanotube structure, achieving excellent optoelectronic performance through its unique structural design. It covers a broad C / C+L spectral range around 1550 nm, effectively absorbing light within this range, while also exhibiting good nonlinear effects, further improving the tunable range of NPR mode-locking, thus significantly enhancing the material's wavelength tuning capability. Furthermore, a dry transfer method was employed during the fabrication of the saturable absorber, successfully achieving a balance between modulation depth and damage threshold, significantly improving the material's performance and stability, and meeting the requirements of high-efficiency lasers.

[0060] Furthermore, the hybrid mode-locked laser of this application achieves a significant performance improvement through innovative NPR tuning and SA-NPR hybrid mode-locking structure. Regarding NPR tuning, by adjusting the polarization controller (PC), traditional external components such as dispersive fibers, gratings, and filters can be replaced, simplifying the system structure and improving system integration and stability. This tuning method not only improves laser performance but also expands its tunable range, enhancing the overall system's flexibility and stability. In terms of the mode-locking structure, traditional mode-locking structures typically rely on a single saturable absorber (SA) for pulse compression, but this structure is susceptible to light intensity fluctuations. This application introduces nonlinear polarization rotation (NPR) technology, combining the synergistic effect of SA and NPR, to achieve dynamic dispersion compensation and enhance nonlinear absorption, thereby making pulse compression more precise and stable. Additionally, by combining phase modulation with the passive mode-locking mechanism of the CNT array, the synergistic effect of high modulation depth and fast recovery time not only increases the tuning center wavelength range but also achieves a narrow pulse width. This innovative hybrid mode-locking mechanism provides the laser with more efficient and stable pulse output, while greatly simplifying the system's complexity.

[0061] The hybrid mode-locked laser of this application can be applied to biomedical imaging, specifically optical coherence tomography (OCT). Due to its wide spectral tuning capability, it supports multi-band OCT, thereby improving axial resolution to <5 μm. The ultrashort pulse (237 fs) effectively reduces thermal effects, achieving sub-micron-level processing accuracy, suitable for precision machining tasks such as semiconductor chip cutting and microfluidic device etching. Furthermore, this application has a high damage threshold (3.5 GW / cm²), supporting high-energy processing, such as sapphire glass drilling, providing strong support for high-precision laser processing. Additionally, it can be applied to scientific research and instrument development; the wide tuning range provided by this application can cover molecular vibrational and electronic transition characteristic peaks, suitable for real-time tracking of chemical reaction dynamics, providing a more efficient and precise laser source for related research fields, and applicable to ultrafast photonics. As a wavelength-tunable femtosecond pulse source, this application can be used to generate entangled photons, supporting quantum key distribution (QKD) and quantum computing research, with significant application prospects, especially in the fields of quantum information processing and secure communication. According to LightCounting's forecast, the global tunable laser market will reach $1.25 billion in 2025, with an annual growth rate (CAGR) of 15%. This application, with its high efficiency and wide wavelength tuning range, is poised to capture 20%-30% of the high-end market share, becoming a core competitive advantage in the optical communication market. According to a report by Grand View Research, the global multiphoton microscope market reached $180 million in 2023. Traditional Ti:sapphire lasers suffer from high cost and complex structures; this application can effectively replace traditional lasers, reducing costs by 50% and providing more efficient and stable performance. Therefore, this application is expected to occupy a significant market share in the biomedical field, especially in high-performance medical imaging and cell imaging.

[0062] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0063] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an array carbon nanotube thin film saturable absorber, characterized in that, The method comprises: dissolving carbon nanotube powder and high molecular polymer in toluene solution to obtain a mixed solution, and performing ultrasonic treatment on the mixed solution by using an ultrasonic machine, and performing centrifugal treatment on the mixed solution after ultrasonic treatment by using a centrifugal machine; depositing the mixed solution after centrifugal treatment on the surface of a substrate by using a solution deposition method to form an array carbon nanotube film, and spin-coating two layers of organic compound layers on one of the surfaces of the substrate on which the array carbon nanotube film is deposited; preparing a transfer solution based on hydrofluoric acid and water, fixing the substrate on which the organic compound layers are spin-coated above the transfer solution, heating the transfer solution, and peeling the array carbon nanotube film and the organic compound layers from the substrate; transferring the array carbon nanotube film and the organic compound layers peeled off to the end face of an optical fiber, naturally air-drying for a preset time, and removing the organic compound layers from the end face of the optical fiber to obtain an array carbon nanotube film saturable absorber.

2. The method for preparing an arrayed carbon nanotube thin film saturable absorber according to claim 1, characterized in that, The method for removing the organic compound layers from the end face of the optical fiber to obtain an array carbon nanotube film saturable absorber comprises: fixing the end face of the optical fiber containing the array carbon nanotube film and the organic compound layers above an acetone solution; heating the acetone solution to remove the organic compound layers on the end face of the optical fiber; air-drying the end face of the optical fiber from which the organic compound layers are removed to obtain an array carbon nanotube film saturable absorber.

3. The method for preparing an arrayed carbon nanotube thin film saturable absorber according to claim 2, characterized in that, The method for spin-coating two layers of organic compound layers on one of the surfaces of the substrate on which the array carbon nanotube film is deposited comprises: vacuum-adsorbing the substrate on which the array carbon nanotube film is deposited on a spin coater; dropping an organic compound solution on one of the surfaces of the substrate and keeping still for a preset time; starting the spin coater and uniformly spin-coating the polyimide solution on the corresponding surface.

4. The method for preparing an arrayed carbon nanotube thin film saturable absorber according to claim 3, characterized in that, The ratio of hydrofluoric acid to water in the transfer solution is 1:18 to 1:22; and / or The rotation speed of the spin coater is 1500 revolutions per second, and the rotation time of the spin coater is one minute.

5. The method for preparing an arrayed carbon nanotube thin film saturable absorber according to claim 1, characterized in that, The array carbon nanotube film is formed by parallel and spaced arrangement of a plurality of single carbon nanotubes.

6. An array carbon nanotube film saturable absorber, characterized in that, The array carbon nanotube film saturable absorber is prepared by using the method for preparing the array carbon nanotube film saturable absorber according to any one of claims 1 to 5.

7. A hybrid mode-locked laser, characterized by The mixed mode laser comprises a pump source, a wavelength division multiplexer, a coupler, a doped fiber, a polarization controller module and the array carbon nanotube film saturable absorber according to claim 6. The output end of the pump source is connected with the input end of the wavelength division multiplexer, the signal light output end of the wavelength division multiplexer is connected with the input end of the array carbon nanotube film saturable absorber, the output end of the array carbon nanotube film saturable absorber is connected with the input end of the coupler, the output end of the coupler is connected with the input end of the polarization controller module, the output end of the polarization controller module is connected with the first end of the doped fiber, and the second end of the doped fiber is connected with the pump light output end of the wavelength division multiplexer.

8. The hybrid mode-locked laser of claim 7, wherein, The polarization controller module comprises a first polarization controller, a polarization dependent polarizer and a second polarization controller, an input end of the first polarization controller is connected with an output end of the coupler, an output end of the second polarization controller is connected with a first end of the DFB, and the polarization dependent polarizer is located between an output end of the first polarization controller and an input end of the second polarization controller. The first polarization controller is used for adjusting a polarization state, and the second polarization controller is used for adjusting a birefringent phase.

9. The hybrid mode-locked laser of claim 8, wherein, The hybrid mode-locked laser further comprises a dispersion compensation module, and the dispersion compensation module is located between the polarization controller module and the DFB.

10. The hybrid mode-locked laser of claim 9, wherein, The dispersion compensation module comprises an SMF-28 optical fiber, and a length of the SMF-28 optical fiber ranges from 1.3 m to 1.8 m.

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