An interference filter type multi-wavelength erbium-doped fiber laser based on optical path difference regulation

Abstract

The application discloses an interference filter type multi-wavelength erbium-doped fiber laser based on optical path difference regulation, relates to the technical field of a ring-shaped tunable multi-wavelength erbium-doped fiber laser, and comprises a pump source, a wavelength division multiplexer, an erbium-doped fiber, an isolator, a first optical fiber coupler, a three-paddle polarization controller, a polarizer, a Mach-Zehnder interferometer filter containing an adjustable delay line, a black phosphorus saturable absorber and an extrusion type polarization controller which constitute a ring cavity. By connecting a 0-6.6 cm continuous adjustable delay line to one arm, the optical path difference of the filter two arms is accurately regulated, and continuous precise tuning of wavelength spacing of 0.3 nm to 1.54 nm is realized; meanwhile, by combining the nonlinear polarization rotation effect and the hybrid mode-locking mechanism of the few-layer black phosphorus, the mode-locking threshold is significantly reduced, and the long-term stability of the pulse is improved. The laser can realize stable emission of up to six wavelengths at the same time, the wavelength drift is less than 0.75 nm, and the power fluctuation is less than 7.0 dB.

Description

Technical Field

[0001] This invention relates to the field of ring-tunable multi-wavelength erbium-doped fiber laser technology, and particularly to an interference-filtered multi-wavelength erbium-doped fiber laser based on optical path difference modulation. Background Technology

[0002] In the field of ring-tunable multi-wavelength erbium-doped fiber laser technology, achieving precise control of wavelength spacing and stable and reliable mode-locked operation for multi-wavelength output is a core technological prerequisite for meeting the application requirements of optical communication, optical sensing, and ultrafast optics. Erbium-doped fiber lasers, due to their operating wavelength covering the 1550nm communication window and ease of implementing ring cavity structures, have become an important platform for realizing multi-wavelength light sources. However, existing technologies still have significant limitations in terms of wavelength spacing control accuracy and long-term mode-locking stability.

[0003] In terms of wavelength selection and spacing control, a common approach is to integrate a conventional Mach-Zehnder Interferometer (MZI) filter into a ring cavity. This utilizes the periodic transmission spectrum caused by the optical path difference between the two arms of the interferometer to select and comb-filter the resonant wavelengths, thus generating multi-wavelength oscillations. Theoretically, the output wavelength spacing can be adjusted by changing the length difference between the two arms of the interferometer. In practical implementation, existing technologies typically rely on mechanical displacement mechanisms to adjust the length of the optical fiber or spatial optical path, such as stretching the fiber or moving the mirror position using a micro-displacement platform. However, this type of mechanical adjustment has inherent limitations: firstly, the adjustment accuracy is limited by the backlash error and resolution of the mechanical transmission components, making it difficult to achieve continuous, sub-micron level fine control of the optical path difference; secondly, mechanical contact adjustment is susceptible to environmental vibrations and temperature drift, leading to unexpected fluctuations in wavelength spacing and poor controllability and repeatability. Especially in scenarios such as high-density wavelength division multiplexing (WDM) where stringent channel spacing accuracy is required, traditional mechanically adjusted MZI filters struggle to guarantee long-term consistency and stability of the multi-wavelength output spectrum.

[0004] Regarding mode-locking mechanisms, existing technologies typically employ one of two approaches or one of them to achieve ultrashort pulse output. The first approach combines an intracavity polarizer with fiber birefringence to create a nonlinear polarization rotation (NPR) effect. By adjusting the polarization controller, the higher peak power portion of the pulse experiences lower losses and is preferentially allowed to pass through, thus achieving passive mode-locking. However, mode-locked lasers based on a single NPR effect usually require high pump power to reach the mode-locking threshold, and the intracavity polarization state is extremely sensitive to environmental disturbances, resulting in poor stability after pulse establishment. During long-term operation, the pulse width, repetition frequency, and output power are prone to slow drift. The second approach involves inserting a two-dimensional material, such as black phosphorus (BP), as a saturable absorber into the cavity, utilizing its intensity-dependent nonlinear absorption characteristics to initiate and maintain mode-locking. Black phosphorus exhibits certain application potential in the near-infrared band due to its high carrier mobility and tunable bandgap. However, existing technologies show that the saturable absorption performance of black phosphorus in the 1550nm operating band of erbium-doped fiber lasers still needs further optimization. Moreover, its two-dimensional layered structure is prone to oxidation and aggregation in air and humid environments, leading to degradation of optical nonlinear response and difficulty in maintaining stable mode-locking state after long-term operation.

[0005] In summary, in the field of ring-tunable multi-wavelength erbium-doped fiber lasers, existing technologies still have shortcomings in terms of precise control of wavelength spacing and long-term stability of mode-locked pulses, which urgently need improvement. Therefore, how to achieve high-precision and repeatable adjustment of the output multi-wavelength spacing, while reducing the mode-locking threshold and improving the long-term reliability of the pulse sequence, has become an important technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address these issues, this invention provides an interferometric filter-based multi-wavelength erbium-doped fiber laser based on optical path difference modulation, which solves the problems of low wavelength interval modulation accuracy, poor controllability, and insufficient mode-locked pulse stability in existing multi-wavelength lasers.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide an interferometric filter-type multi-wavelength erbium-doped fiber laser based on optical path difference modulation, comprising: [the following components] forming a ring cavity: One pump source; A wave division multiplexer, wherein the pump input is connected to the output of the pump source; An erbium-doped optical fiber is used as the gain medium, and its input end is connected to the common end of the wavelength division multiplexer. An isolator, the input of which is connected to the output of the erbium-doped fiber, is used to ensure unidirectional transmission of optical signals; A first fiber optic coupler, whose input end is connected to the output end of the isolator, is used to split the optical signal into two paths. Its first output end is used to output laser light, and its second output end is used for intracavity circulation of the optical signal. A three-paddle polarization controller, the input of which is connected to the second output of the first fiber coupler; A polarizer, whose input is connected to the output of the three-paddle polarization controller, is used to adjust the polarization state of the optical signal; A Mach-Zehnder interferometer filter, the input of which is connected to the output of the polarizer, is used for the selection and spacing control of multiple wavelengths; A black phosphorus saturable absorber, the input of which is connected to the output of the Mach-Zehnder interferometer filter; A squeeze-type polarization controller, whose input end is connected to the output end of the black phosphorus saturable absorber, and whose output end is connected back to the ring cavity feedback port of the wavelength division multiplexer to form a closed-loop ring resonant cavity. The Mach-Zehnder interferometer filter includes an adjustable delay line connected to one arm. By adjusting the adjustable delay line, the optical path difference between the two arms of the filter can be changed, thereby achieving continuous and precise control of the output wavelength interval. The annular cavity combines the nonlinear polarization rotation effect formed by the polarizer, the three-paddle polarization controller, and the squeeze polarization controller with the nonlinear absorption effect of the black phosphorus saturable absorber to form a hybrid mode-locking effect, thereby generating highly stable multi-wavelength pulsed laser output.

[0008] Preferably, the Mach-Zehnder interferometer filter specifically includes: A second fiber optic coupler, whose input end serves as the input end of the filter, is used to split the input light into two paths; A first interferometer arm connected to the adjustable delay line has its input end connected to the first beam splitting output end of the second fiber coupler. A reference fiber arm serves as the second interference arm, with its input end connected to the second beam splitting output end of the second fiber coupler, to provide an equal-length matched optical path reference. A third fiber optic coupler, whose two input ends are respectively connected to the output ends of the first interferometer and the second interferometer, is used to combine and interfere the two optical signals, and its output end serves as the output end of the filter.

[0009] Preferably, the adjustable delay line has a continuous adjustment range of 0 to 6.6 cm, and the optical path difference between the two arms is precisely controlled by changing the physical length of the optical fiber connected to the first interferometer arm. This allows for the adjustment of the output laser wavelength interval. The fine adjustment of the relationship satisfies the formula: ; in, For the operating wavelength, This represents the effective refractive index of the optical fiber.

[0010] Preferably, the hybrid mode-locking is achieved by the coordinated action of the three-paddle polarization controller, the polarizer, the squeeze polarization controller, and the black phosphorus saturable absorber disposed within the cavity; wherein, the three-paddle polarization controller and the polarizer jointly complete the initial control and selection of polarization state, the black phosphorus saturable absorber provides a nonlinear saturable absorption effect, and the squeeze polarization controller performs secondary optimization of polarization state on the optical signal within the feedback loop.

[0011] Preferably, the black phosphorus saturable absorber is made of few-layer black phosphorus material, which works in conjunction with the nonlinear polarization rotation effect to reduce the mode-locking threshold of the laser and enhance the long-term stability of the mode-locked pulse.

[0012] Preferably, the erbium-doped fiber is a highly doped fiber with a peak absorption coefficient at 1530 nm. dB / m, with a length of 1 meter, is used to provide efficient gain for 1550nm band signal light under 980nm pump light.

[0013] Preferably, the pump source is a 980nm semiconductor laser, and the wavelength division multiplexer is a 980 / 1550nm wavelength division multiplexer.

[0014] Preferably, the laser changes the optical path difference between the two arms by adjusting the adjustable delay line. It can achieve continuously tunable multi-wavelength laser output with wavelength spacing ranging from 0.3nm to 1.54nm.

[0015] Preferably, under stable operating conditions with a pump power of 103.3mW, the laser can achieve simultaneous stable lasing of up to six wavelengths, and within a long observation period of 50 minutes, the output wavelength drift is less than 0.75nm, and the power fluctuation amplitude of each wavelength channel is less than 7.0dB.

[0016] As can be seen from the above technical solutions, this invention application has the following beneficial effects: First, this invention incorporates a continuously manually adjustable delay line (0-6.6 cm) into one arm of a Mach-Zehnder interferometer filter, allowing for precise adjustment of the optical path difference between the two arms. Achieve output wavelength spacing With precise control, the wavelength spacing can be adjusted from 0.3nm to 1.54nm. Compared with traditional mechanical adjustment methods, this solution overcomes the shortcomings of low adjustment accuracy, poor controllability, and insufficient repeatability, and can meet the stringent requirements for wavelength spacing accuracy in scenarios such as high-density wavelength division multiplexing.

[0017] Secondly, this invention employs a hybrid mode-locking mechanism combining nonlinear polarization rotation effect with a few-layer black phosphorus saturable absorber. It leverages the excellent nonlinear optical properties of black phosphorus to effectively reduce the mode-locking threshold, while the flexible control of the polarization controller compensates for the susceptibility of single mode-locking technologies to environmental disturbances. Experiments show that under stable operating conditions with a pump power of 103.3 mW, simultaneous lasing of up to six wavelengths can be achieved, with wavelength drift less than 0.75 nm and power fluctuation less than 7.0 dB within 50 minutes, significantly improving long-term pulse stability.

[0018] Third, the present invention incorporates both squeeze-type and three-paddle-type polarization controllers within the annular cavity, which can collaboratively adjust the polarization state distribution within the cavity, further expanding the tunable wavelength range and ensuring stable oscillation of multi-wavelength lasers. Through the combined adjustment of the adjustable delay line and the polarization controller, the number and spacing of output wavelengths can be flexibly changed, while ensuring the high-quality characteristics of the output pulses. This has broad application prospects in fields such as optical communication, optical sensing, and ultrafast optics. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Referring to the drawings will make the features and advantages of the present invention clearer. The drawings are illustrative and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the structure of an interferometric filter-type erbium-doped fiber laser based on optical path difference modulation provided by the present invention; Figure 2 This is a schematic diagram of the MZI filter with adjustable delay line in this invention; Figure 3 This is a simulation diagram of the transmission spectrum of the Mach-Zehnder interferometer filter when the wavelength intervals are 1.54nm, 1.28nm, 0.8nm, 0.58nm and 0.3nm respectively. Figure 4 These are experimental diagrams of the transmission spectrum of the Mach-Zehnder interferometer filter when the wavelength intervals are 1.54 nm, 1.28 nm, 0.8 nm, 0.58 nm and 0.3 nm, respectively. Among them, (a), (b), (c), (d) and (e) are experimental diagrams at 1.54 nm, 1.28 nm, 0.8 nm, 0.58 nm and 0.3 nm, respectively. Figure 5 These are multi-wavelength spectral images of different modulation periods of 1.28 nm when the pump power is 103.3 mW in this invention; Figure 6 These are multi-wavelength spectral images of different modulation periods of 0.8 nm when the pump power is 103.3 mW in this invention; Figure 7 These are multi-wavelength spectral images of different modulation periods of 0.58 nm when the pump power is 103.3 mW in this invention. Figure 8 This invention describes the wavelength drift and power fluctuation over 50 minutes, where (a) is a schematic diagram of wavelength drift and (b) is a schematic diagram of power fluctuation.

[0020] Explanation of reference numerals in the accompanying drawings: 1. Pump source; 2. Wavelength division multiplexer; 3. Erbium-doped fiber; 4. Isolator; 5. First fiber coupler; 6. Three-paddle polarization controller; 7. Polarizer; 8. Second fiber coupler; 9. Adjustable delay line; 10. Third fiber coupler; 11. Black phosphorus saturable absorber; 12. Squeezed polarization controller. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: To address the problems of low wavelength spacing control precision, poor controllability, and insufficient mode-locked pulse stability in existing multi-wavelength laser technologies, this invention proposes an interferometric filter-based multi-wavelength erbium-doped fiber laser based on optical path difference control. For example... Figure 1 As shown, the laser includes the following components forming a ring cavity: Pump source 1, specifically a 980nm semiconductor laser; Wavelength division multiplexer 2 (WDM) is a 980 / 1550nm wavelength division multiplexer, and its pump input is connected to the output of pump source 1. An erbium-doped fiber 3 serves as the gain medium, with its input end connected to the common end of the wavelength division multiplexer 2. The erbium-doped fiber 3 is a highly doped fiber (model Er80-8 / 125) with a peak absorption coefficient of [value missing] at 1530 nm. dB / m, with a length of 1 meter, is used to provide efficient gain for 1550nm band signal light under 980nm pump light; An isolator 4 (ISO) is connected to the output of the erbium-doped fiber 3 to ensure unidirectional transmission of optical signals and prevent backlight interference with the stable operation of the laser. A first optical fiber coupler 5 (OC) is a 10:90 optical fiber coupler (10% OC). Its input end is connected to the output end of the isolator 4. It is used to split the optical signal into two paths. Its first output end (10% port) is used to output 10% of the optical power to external test instruments to monitor the laser performance. Its second output end (90% through end) is used to feed 90% of the optical power back into the ring cavity for continued cyclic amplification. A three-paddle polarization controller 6, the input of which is connected to the second output of the first fiber coupler 5; A polarizer 7, whose input is connected to the output of the three-paddle polarization controller 6, is used to adjust the polarization state of the optical signal, thereby optimizing mode selection characteristics and improving mode-locking stability. A Mach-Zehnder interferometer filter (MZI filter) is connected to the output of the polarizer 7 and is used to select and space multiple wavelengths. A black phosphorus saturable absorber 11 (BP-SA) has its input terminal connected to the output terminal of the Mach-Zehnder interferometer filter. A compression polarization controller 12 has its input end connected to the output end of the black phosphorus saturable absorber 11, and its output end connected back to the ring cavity feedback port of the wavelength division multiplexer 2 to form a complete closed-loop ring resonant cavity, thereby realizing continuous oscillation and stable output of the laser.

[0023] The Mach-Zehnder interferometer filter includes an adjustable delay line 9 connected to one arm. By adjusting the adjustable delay line 9, the optical path difference between the two arms of the filter can be changed, thereby achieving continuous and precise control of the output wavelength interval.

[0024] The annular cavity, through the nonlinear polarization rotation (NPR) effect formed by the polarizer 7, the three-paddle polarization controller 6, and the squeeze polarization controller 12, combined with the nonlinear absorption effect of the black phosphorus saturable absorber 11, forms a hybrid mode-locking mechanism to generate pulsed laser output with high stability, narrow pulse width, and excellent spectral characteristics. The squeeze and three-paddle polarization controllers installed in the cavity work together to flexibly adjust the polarization state within the cavity, further expanding the tunable wavelength range and ensuring stable oscillation of multi-wavelength lasers.

[0025] In this embodiment, the specific structure of the Mach-Zehnder interferometer filter is as follows: Figure 2 As shown, it includes: A second fiber optic coupler 8 (50% OC, 3dB coupler) has its input end serving as the input end of the filter and is connected to the output end of the polarizer 7 to split the input light into two paths with equal power. A first interferometer arm connected to the adjustable delay line 9 has its input end connected to the first beam splitting output end of the second fiber coupler 8. A reference fiber arm serves as the second interference arm, with its input end connected to the second beam splitting output end of the second fiber coupler 8, to provide an equal-length matched optical path reference. A third fiber optic coupler 10 (50% OC, 3dB coupler) has its two input terminals connected to the output terminals of the first interferometer and the second interferometer, respectively, for combining and interfering the two optical signals. Its output terminal serves as the output terminal of the filter and is connected to the input terminal of the black phosphorus saturable absorber 11.

[0026] The adjustable delay line 9 has a continuous manual adjustment range of 0 to 6.6 cm. By changing the physical length of the optical fiber connected to the first interferometer arm, the optical path difference ΔL between the two arms can be precisely controlled, thereby achieving fine adjustment of the output laser wavelength interval Δλ. Its control principle satisfies the following formula (1): (1) in, For the operating wavelength, This represents the effective refractive index of the optical fiber.

[0027] in, The operating wavelength is approximately 1550 nm. The effective refractive index of the single-mode fiber is 1.45 (usually taken as 1.45). From formula (1), the optical path difference between the two arms is... The larger the wavelength spacing The smaller the value, the greater the value; conversely, the larger the value, the greater the value. Therefore, by continuously adjusting the adjustable delay line 9, the value can be changed. This enables continuous and precise control of the output wavelength interval, overcoming the shortcomings of traditional mechanical adjustment methods, such as low precision, poor controllability, and poor repeatability.

[0028] Fabrication and performance testing of MZI filters: The specific fabrication process of the MZI filter in this embodiment is as follows. Figure 2As shown, the adjustable delay line 9 is connected to one arm of a standard MZI filter. Since the input (in) and output (out) ends of the adjustable delay line 9 each have 1 meter of fiber, a 2-meter length of standard single-mode fiber needs to be added to the reference arm to achieve equal-length matching. Furthermore, considering the slight length error that may be introduced during fiber splicing, the initial scale of the adjustable delay line 9 is adjusted to 3.3 cm before being connected to the optical path. An additional 3 cm of fiber is added to the reference arm for compensation to ensure that the two arms are of equal length initially. The MZI filter constructed in this way allows for bidirectional fine-tuning of the optical path difference by adjusting the delay line in one arm connected to the adjustable delay line 9, enabling both increasing and decreasing the optical path.

[0029] The completed MZI filter was connected to a 1550nm pump light source for performance testing. The wavelength interval between adjacent peaks in the output spectrum was read and substituted into formula (1) to deduce the actual optical path difference between the two arms. By adjusting the adjustable delay line 9, when the time delay corresponding to the delay line reading is about 210ps, the filter reaches the maximum modulation period (the modulation period is about 8.5nm when the input power is 15mW). At this time, the optical path difference between the two arms of the MZI filter is the smallest, about 0.19mm.

[0030] To verify the wavelength spacing control characteristics of the filter, this invention first conducted numerical simulations. Figure 3 The simulated transmission spectrum of the MZI filter, where the wavelength spacing is... The corresponding optical path differences between the two arms are 1.54nm, 1.28nm, 0.8nm, 0.58nm, and 0.3nm, respectively. The optical path differences are approximately 1.10 mm, 1.30 mm, 2.10 mm, 2.90 mm, and 5.50 mm, respectively. Simulation results clearly show the optical path difference between the two arms. The larger the value, the smaller the modulation period of the filter, which means the smaller the wavelength interval.

[0031] Experimental tests were conducted under simulation guidance. Fine-tuning was performed on one arm of the MZI filter with the added adjustable delay line 9 to ensure its optical path difference matched the simulation result. The values ​​are consistent. Figure 4 Middle (a) to Figure 4 Figure (e) presents the experimental measurement results of the transmission spectrum of the MZI filter at wavelength intervals of 1.54 nm, 1.28 nm, 0.8 nm, 0.58 nm, and 0.3 nm. The experimentally measured spectra are consistent with... Figure 3 The simulation results are in high agreement, confirming that the MZI filter with adjustable delay line 9 described in this invention can achieve continuous and precise control of wavelength spacing in the range of 0.3nm to 1.54nm.

[0032] Implementation and testing of multi-wavelength laser output characteristics: The MZI filter prepared and verified above is connected to... Figure 1 Inside the ring laser cavity shown. At the beginning of the experiment, the optical path difference was set according to the preset wavelength interval requirements via the adjustable delay line 9. Start pump source 1 and gradually increase the pump power. When the pump current reaches 260mA (corresponding to a pump power of approximately 103.3mW), the ring cavity reaches the laser oscillation threshold and begins to generate laser output.

[0033] By coordinating the three-paddle polarization controller 6 and the squeeze-type polarization controller 12, the polarization state distribution within the laser cavity can be effectively altered, thereby controlling the gain and loss relationship of different longitudinal modes. Without optimized adjustment of the polarization controllers, only a single-wavelength lasing mode is observed in the output spectrum. As the polarization controllers are gradually finely adjusted, the gains of each longitudinal mode within the cavity tend to become more balanced, new wavelength channels are successively excited and stabilize, and the output spectrum sequentially exhibits simultaneous lasing characteristics of two wavelengths, three wavelengths, and even six wavelengths.

[0034] Figure 5 The following conditions are given: pump power of 103.3mW, MZI filter modulation period (wavelength spacing) set to 1.28nm (at this time...). Under conditions of approximately 1.29 mm, spectral images of single-wavelength to six-wavelength simultaneous outputs were obtained sequentially by adjusting the polarization controller. Six stable lasing wavelength channels can be clearly distinguished from the images.

[0035] Subsequently, the adjustable delay line 9 was slowly adjusted to make the optical path difference between the two arms of the MZI equal. When the wavelength is increased to 2.07 mm, the output wavelength spacing becomes 0.8 nm according to formula (1). Figure 6 This demonstrates the evolution of the output spectrum from single wavelength to six wavelengths under these conditions. Continuing to increase the adjustment of the tunable delay line 9, when... When the wavelength is increased to 2.86 mm, the wavelength spacing is further reduced to 0.58 nm, and its multi-wavelength output spectrum is as follows: Figure 7 As shown, the maximum number of output wavelengths can still be stably maintained at six.

[0036] The above experimental results show that the laser of the present invention, through the synergistic effect of the MZI filter with adjustable delay line 9 and the hybrid mode-locking structure, can not only achieve continuous and precise tuning of wavelength intervals under a fixed pump power, but also maintain stable simultaneous lasing of up to six wavelengths under different wavelength intervals.

[0037] Long-term stability testing: To verify the stability of the laser of the present invention under long-term operating conditions, the output spectrum of the laser was continuously monitored with the pump power stabilized at 103.3mW and the initial output wavelength interval set at about 0.8nm, and the data was recorded at 10-minute intervals. Figure 8 The center wavelength drift of multiple output wavelength channels was shown separately during a 50-minute continuous observation period. Figure 8 (a) and the corresponding power fluctuation situation ( Figure 8 (b)). Seven stable wavelength channels were recorded in the experiment.

[0038] from Figure 8 As can be seen in (a), all wavelength channels remained at relatively stable wavelength positions throughout the entire 50-minute observation period, exhibiting only slight periodic fluctuations. The maximum wavelength drift was less than 0.75 nm, indicating that the laser possesses excellent wavelength stability under long-term operating conditions. Meanwhile, Figure 8 The power curve shown in (b) shows that the power fluctuation amplitude of each wavelength channel is less than 7.0 dB, which further proves that the laser of the present invention also has good long-term stability in terms of output power.

[0039] The above experimental data fully demonstrates the effectiveness of the technical solution proposed in this invention: by introducing an adjustable delay line 9 from 0 to 6.6 cm into one arm of the MZI filter, the optical path difference between the two arms is effectively controlled. The invention achieves fine-tuning, enabling continuous and precise control of wavelength intervals within the range of 0.3 nm to 1.54 nm, overcoming the shortcomings of low precision and poor controllability of traditional mechanical adjustment methods. It employs a hybrid mode-locking device combining "nonlinear polarization rotation (NPR) + few-layer black phosphorus (BP)," which utilizes the excellent nonlinear optical properties of black phosphorus to lower the mode-locking threshold while compensating for the susceptibility of single mode-locking techniques to environmental interference through polarization control, thus realizing highly stable, narrow-pulse-width multi-wavelength mode-locked pulse output. The ring-shaped tunable multi-wavelength erbium-doped fiber laser provided by this invention has broad application prospects in optical communication, optical sensing, high-density wavelength division multiplexing, and ultrafast optics.

[0040] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An interferometric filter-type erbium-doped fiber laser based on optical path difference modulation, characterized in that, Including the components that make up the annular cavity: One pump source (1); A wave division multiplexer (2) has its pump input terminal connected to the output terminal of the pump source (1); An erbium-doped fiber (3) serves as the gain medium, and its input end is connected to the common end of the wavelength division multiplexer (2). An isolator (4) is connected at its input end to the output end of the erbium-doped fiber (3) to ensure unidirectional transmission of optical signals; A first fiber optic coupler (5) has its input end connected to the output end of the isolator (4) to split the optical signal into two paths. Its first output end is used to output laser, and its second output end is used for intracavity circulation of the optical signal. A three-paddle polarization controller (6) has its input end connected to the second output end of the first fiber coupler (5); A polarizer (7) is connected at its input to the output of the three-paddle polarization controller (6) to adjust the polarization state of the optical signal; A Mach-Zehnder interferometer filter, the input of which is connected to the output of the polarizer (7), is used to select and space multiple wavelengths; A black phosphorus saturable absorber (11) has its input end connected to the output end of the Mach-Zehnder interferometer filter; A squeeze-type polarization controller (12) has its input end connected to the output end of the black phosphorus saturable absorber (11) and its output end connected back to the ring cavity feedback port of the wavelength division multiplexer (2) to form a closed-loop ring resonant cavity. The Mach-Zehnder interferometer filter includes an adjustable delay line (9) connected to one arm. By adjusting the adjustable delay line (9), the optical path difference between the two arms of the filter can be changed, thereby achieving continuous and precise control of the output wavelength interval. The annular cavity combines the nonlinear polarization rotation effect formed by the polarizer (7), the three-paddle polarization controller (6), and the squeeze polarization controller (12) with the nonlinear absorption effect of the black phosphorus saturable absorber (11) to form a hybrid mode lock, thereby generating highly stable multi-wavelength pulsed laser output.

2. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The Mach-Zehnder interferometer filter specifically includes: A second fiber optic coupler (8) is used as the input of the filter to split the input light into two paths. A first interferometer arm connected to the adjustable delay line (9) has its input end connected to the first beam splitting output end of the second fiber coupler (8); A reference arm fiber serves as the second interference arm, with its input end connected to the second beam splitting output end of the second fiber coupler (8) to provide an equal-length matching optical path reference. A third fiber optic coupler (10) has two input ends connected to the output ends of the first interferometer and the second interferometer, respectively, for combining and interfering the two optical signals, and its output end serves as the output end of the filter.

3. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The adjustable delay line (9) has a continuous adjustment range of 0 to 6.6 cm, and the optical path difference between the two arms can be precisely controlled by changing the physical length of the optical fiber connected to the first interferometer arm. This allows for the adjustment of the output laser wavelength interval. The fine adjustment of the relationship satisfies the formula: ； in, For the operating wavelength, This represents the effective refractive index of the optical fiber.

4. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The hybrid mode-locking is achieved by the coordinated action of the three-paddle polarization controller (6), the polarizer (7), the squeeze polarization controller (12), and the black phosphorus saturable absorber (11) located in the cavity; wherein, the three-paddle polarization controller (6) and the polarizer (7) jointly complete the initial control and selection of polarization state, the black phosphorus saturable absorber (11) provides nonlinear saturable absorption effect, and the squeeze polarization controller (12) performs secondary optimization of polarization state of the optical signal in the feedback loop.

5. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 4, characterized in that, The black phosphorus saturable absorber (11) is made of few-layer black phosphorus material, which works in conjunction with the nonlinear polarization rotation effect to reduce the mode-locking threshold of the laser and enhance the long-term stability of the mode-locked pulse.

6. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The first fiber coupler (5) is a 10:90 fiber coupler. Its second output end is a straight-through end, which is used to feed 90% of the optical power back into the ring cavity for continued cyclic amplification. Its first output end is used to output 10% of the optical power to external test instruments.

7. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The erbium-doped fiber (3) is a highly doped fiber with a peak absorption coefficient at 1530 nm of [value missing]. dB / m, with a length of 1 meter, is used to provide efficient gain for 1550nm band signal light under 980nm pump light.

8. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The pump source (1) is a 980nm semiconductor laser, and the wavelength division multiplexer (2) is a 980 / 1550nm wavelength division multiplexer.

9. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, The laser changes the optical path difference between the two arms by adjusting the adjustable delay line (9). It can achieve continuously tunable multi-wavelength laser output with wavelength spacing ranging from 0.3nm to 1.54nm.

10. The interferometric filter-type erbium-doped fiber laser based on optical path difference control according to claim 1, characterized in that, Under stable operating conditions with a pump power of 103.3mW, the laser can achieve stable simultaneous lasing of up to six wavelengths, and within a long observation period of 50 minutes, the output wavelength drift is less than 0.75nm, and the power fluctuation amplitude of each wavelength channel is less than 7.0dB.

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