Erbium-doped fiber mode-locked laser started by seed injection

Abstract

The invention discloses an erbium-doped fiber mode-locked laser started by seed injection. Wherein the seed laser, the energy regulator, the space-optical fiber coupler, the spectrum broadening optical fiber, the first optical fiber coupler and the first filter are connected in sequence to form a seed injection starting device; the first optical fiber coupler, the first filter, the isolator, the first wavelength division multiplexer, the first erbium-doped optical fiber, the second optical fiber coupler, the second filter, the second wavelength division multiplexer and the second erbium-doped optical fiber are sequentially connected in an optical fiber fusion welding mode to form an all-optical-fiber annular resonant cavity; the all-fiber annular resonant cavity, the first pumping source and the second pumping source form a mode-locked oscillator; and mode-locked pulse output is realized through the mode-locked oscillator. The nanosecond pulse emitted by the seed laser is regulated and injected into the mode-locked laser, so that low-cost, efficient and reliable passive mode-locked starting and high-energy ultrafast pulse generation are realized.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber lasers, and in particular to an erbium-doped optical fiber mode-locked laser started by seed injection. Background Art

[0002] Erbium-doped fiber mode-locked lasers can generate ultrafast laser pulses in the 1550 nm band, which has important application value in the fields of lidar, bio-imaging, and precision metrology. In recent years, the Mamyshev mode-locked mechanism based on intracavity self-phase modulation (SPM) and spectral filtering effects has attracted widespread attention due to its high output pulse energy and good environmental stability. However, since the Mamyshev mechanism has a strong suppression effect on intracavity noise, it is difficult to start the mode-locked state spontaneously, and additional means are usually required to promote the start of the mode-locked process. Among them, seed injection is an effective starting method, which helps start the mode-locked operation by introducing external picosecond (ps) ultrafast laser pulses.

[0003] However, the external light sources that provide such ultrafast pulses (such as gain-switched laser diodes or mode-locked lasers) are often complex and expensive, which poses a challenge to practical applications. At present, researchers have developed a low-cost, simple and reliable seed injection startup scheme using a 100-picosecond passively Q-switched microchip laser as a seed source, but in the 1550-nanometer band, due to the lack of a suitable 100-picosecond seed source and differences in fiber dispersion characteristics, it is still mainly dependent on the establishment of a mode-locked laser to provide an external seed source to output ultrafast pulses for seed injection startup. Summary of the invention

[0004] The purpose of the present invention is to provide a seed injection started erbium-doped fiber mode-locked laser to solve the problem of requiring an expensive and complex external seed source in the traditional seed injection started Mamyshev mechanism erbium-doped fiber mode-locked laser, thereby achieving low-cost seed injection start and high-performance ultrashort pulse generation in the 1550nm band.

[0005] The first aspect of the present invention provides a seed injection-started erbium-doped fiber mode-locked laser, comprising: a seed laser (1), an energy regulator (2), a space-fiber coupler (3), a spectrum broadening fiber (4), a first fiber coupler (5), a first filter (6), an isolator (7), a first pump source (8), a first wavelength division multiplexer (9), a first erbium-doped fiber (10), a second fiber coupler (11), a second filter (12), a second pump source (13), a second wavelength division multiplexer (14) and a second erbium-doped fiber (15);

[0006] The seed laser (1), the energy regulator (2), the space-fiber coupler (3), the spectrum-broadening fiber (4), the first fiber coupler (5) and the first filter (6) are connected in sequence to form a seed injection start-up device; in the seed injection start-up device, the seed pulse emitted by the seed laser is used to start the mode-locked laser after being spectrum-broadened by the spectrum-broadening fiber (4) and spectrum-filtered by the first filter (6);

[0007] The first optical fiber coupler (5), the first filter (6), the isolator (7), the first wavelength division multiplexer (9), the first erbium-doped optical fiber (10), the second optical fiber coupler (11), the second filter (12), the second wavelength division multiplexer (14) and the second erbium-doped optical fiber (15) are connected in sequence by optical fiber fusion splicing to form an all-fiber ring resonator; the all-fiber ring resonator and the first pump source (8) and the second pump source (13) form a mode-locked oscillator; and mode-locked pulse output is achieved through the mode-locked oscillator.

[0008] Furthermore, in the seed injection start-up device, the seed pulse output by the seed laser (1) has the following characteristics:

[0009] The central wavelength is within the range of 1530-1540nm or 1560-1570nm;

[0010] The pulse width is between 1 and 100 ns;

[0011] The peak power is greater than 1kW.

[0012] Furthermore, the energy regulator (2) is used to regulate the energy of the seed pulse output by the seed laser (1); the energy regulation accuracy of the energy regulator is not less than 5% of the original energy of the seed pulse.

[0013] Furthermore, the space-fiber coupler (3) is used to shrink the seed pulse output by the seed laser (1), limit the spot of the seed pulse to a size comparable to the diameter of the optical fiber core, and inject it into the spectrum broadening optical fiber (4).

[0014] Furthermore, the spectrum-broadening optical fiber (4) is used to cause nonlinear spectrum broadening of the seed pulse output by the seed laser (1) and generate spectrum sideband components outside the central wavelength; the spectrum broadening amount of the nonlinear spectrum broadening is regulated by the adjustment amount of the energy regulator (2) and the type and length of the spectrum-broadening optical fiber (4).

[0015] Furthermore, the seed pulse output by the seed laser (1) is incident through an input end of the first optical fiber coupler (5) and enters the mode-locked oscillator.

[0016] Furthermore, the first filter (6) and the second filter (12) are bandpass filters with bandwidths in the order of nm; the central wavelength of the first filter (6) is adjustable at least within the range of 1545 to 1549 nm or 1551 to 1555 nm, and the bandpass frequency band of the first filter (6) does not include the central wavelength of the seed pulse before spectrum broadening, so that the seed pulse retains only a small amount of spectral sideband components after passing through the first filter (6).

[0017] Furthermore, the first pump source (8) outputs pump light that is incident on the mode-locked oscillator through the first wavelength division multiplexer (9); the second pump source (13) outputs pump light that is incident on the mode-locked oscillator through the second wavelength division multiplexer (14);

[0018] The first pump source (8) and the second pump source (13) output pump light in the 980 nm band or the 1480 nm band.

[0019] Furthermore, the first erbium-doped optical fiber (10) and the second erbium-doped optical fiber (15) are polarization-maintaining optical fibers that exhibit normal dispersion characteristics in a range of at least 1540 to 1560 nm.

[0020] Furthermore, the operating frequency band of the first optical fiber coupler (5), the isolator (7), the first wavelength division multiplexer (9), the first erbium-doped optical fiber (10), the second optical fiber coupler (11), the second filter (12), the second wavelength division multiplexer (14) and the second erbium-doped optical fiber (15) is 1550 nm.

[0021] The embodiments of the present invention have the following beneficial effects: the present invention uses a seed injection-started erbium-doped fiber mode-locked laser with a pulse width in the nanosecond (ns) level, and realizes low-cost, stable and reliable seed injection-started mode locking by controlling the spectrum broadening of the seed pulse and filtering out the useless components that occupy most of the energy. The present invention can realize stable and high-performance ultrafast pulse generation by constructing an all-fiber ring Mamyshev oscillator cavity, and simplifies the laser structure by sharing a fiber coupler and a filter with a seed injection starter device.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 The present invention is a schematic structural diagram of an erbium-doped fiber mode-locked laser started by seed injection according to an embodiment of the present invention.

[0025] Figure 2 This is a measured diagram of seed pulse spectrum broadening provided according to an embodiment of the present invention.

[0026] Figure 3 This is a measured diagram of a pulse sequence output by a laser mode-locking device according to an embodiment of the present invention.

[0027] Figure 4 This is a measured spectrum diagram of the mode-locked output of the laser provided according to an embodiment of the present invention at different pulse energies.

[0028] Figure numerals: 1-seed laser, 2-energy regulator, 3-space-fiber coupler, 4-spectrum broadening fiber, 5-first fiber coupler, 6-first filter, 7-isolator, 8-first pump source, 9-first wavelength division multiplexer, 10-first erbium-doped fiber, 11-second fiber coupler, 12-second filter, 13-second pump source, 14-second wavelength division multiplexer, 15-second erbium-doped fiber. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, the first aspect of the present invention provides a seed injection-started erbium-doped fiber mode-locked laser, comprising: a seed laser 1, an energy regulator 2, a space-fiber coupler 3, a spectrum broadening fiber 4, a first fiber coupler 5, a first filter 6, an isolator 7, a first pump source 8, a first wavelength division multiplexer 9, a first erbium-doped fiber 10, a second fiber coupler 11, a second filter 12, a second pump source 13, a second wavelength division multiplexer 14 and a second erbium-doped fiber 15;

[0031] The seed laser 1, the energy regulator 2, the space-fiber coupler 3, the spectrum-broadening fiber 4, the first fiber coupler 5 and the first filter 6 are connected in sequence to form a seed injection start-up device; in the seed injection start-up device, the seed pulse emitted by the seed laser is used to start the mode-locked laser after being spectrum-broadened by the spectrum-broadening fiber 4 and spectrum-filtered by the first filter 6;

[0032] The first fiber coupler 5, the first filter 6, the isolator 7, the first wavelength division multiplexer 9, the first erbium-doped fiber 10, the second fiber coupler 11, the second filter 12, the second wavelength division multiplexer 14 and the second erbium-doped fiber 15 are sequentially connected by fiber fusion to form an all-fiber ring resonator; the all-fiber ring resonator and the first pump source 8 and the second pump source 13 form a mode-locked oscillator; the mode-locked pulse output is achieved through the mode-locked oscillator. In the mode-locked oscillator of the embodiment of the present invention, the mode-locked pulse output is achieved through the Mamyshev mechanism with self-phase modulation and spectrum filtering.

[0033] The Mamyshev mechanism refers to a passive mode-locking technology used in mode-locked lasers. The mode-locking technology locks multiple longitudinal mode light waves together so that they overlap in time and interfere to form ultrashort pulses. The characteristic of the Mamyshev mechanism is that it uses the self-phase modulation (SPM) effect of light and the spectrum filtering effect to achieve mode locking.

[0034] An oscillator that achieves mode locking using the Mamyshev mechanism is generally referred to as a Mamyshev oscillator. Specifically, it consists of two Mamyshev regenerators. A single Mamyshev regenerator consists of a medium that acts as a self-phase modulation spectrum broadener and a bandpass filter. Connecting two Mamyshev regenerators end to end, and offsetting the center wavelengths of the two bandpass filters and separating the passband frequency bands, a Mamyshev oscillator is formed. This structure can withstand high nonlinear phase shifts, thereby supporting the generation of high-energy ultrafast pulses. At the same time, due to the offset of the center wavelength of the filter, it has a strong ability to suppress continuous noise, thereby ensuring the stable operation of the mode lock.

[0035] In the embodiment of the present invention, the first wavelength division multiplexer 9, the first erbium-doped fiber 10, the second fiber coupler 11 and the second filter 12 constitute a first regenerator, and the second wavelength division multiplexer 14, the second erbium-doped fiber 15, the first fiber coupler 5 and the first filter 6 constitute a second regenerator; at the same time, the central wavelengths and frequency bands of the first filter 6 and the second filter 12 are separated, so that the mode-locked oscillator of the embodiment of the present invention can realize the mode-locked pulse output of the Mamyshev mechanism.

[0036] Specifically, in the seed injection start-up device, the seed pulse output by the seed laser 1 has the following characteristics:

[0037] The central wavelength is within the range of 1530-1540nm or 1560-1570nm;

[0038] The pulse width is between 1 and 100 ns;

[0039] The peak power is greater than 1kW.

[0040] The seed laser 1 used in the embodiment of the present invention is a passively Q-switched erbium-doped glass laser, and the central wavelength of the output seed pulse laser is 1533.6nm, the bandwidth is less than 0.2nm, the pulse energy is 120μJ, the pulse width is about 4ns, the peak power is about 30kW, and the repetition frequency is adjustable from 1 to 20Hz. In addition to the Er glass laser mentioned in the embodiment of the present invention, a gain-switched laser diode + power amplified laser, a fiber passively Q-switched laser, and other seed lasers can also be used to output seed pulse lasers.

[0041] The energy regulator 2 is used to adjust the energy of the seed pulse output by the seed laser 1; the energy adjustment accuracy of the energy regulator is not less than 5% of the original energy of the seed pulse; for example, when the seed pulse energy is 120 μJ, the adjustment accuracy is ≦6 μJ to achieve high-precision energy adjustment. In the embodiment of the present invention, the energy regulator 2 is composed of a half-wave plate and a polarization beam splitter cube. By rotating the half-wave plate, the laser energy of the seed pulse output by the seed laser can be continuously adjusted, thereby regulating the spectrum broadening in the subsequent optical fiber propagation process. Optionally, a gradient neutral density filter can also be used as an energy regulator.

[0042] The space-fiber coupler 3 is used to shrink the seed pulse output by the seed laser 1, limit the spot of the seed pulse to a size comparable to the diameter of the optical fiber core, and inject it into the spectrum broadening optical fiber 4. In the embodiment of the present invention, the space-fiber coupler 3 is composed of a plano-convex lens (focal length f=200mm) and a fiber collimator. After the plano-convex lens collimates the output laser of the seed laser 1, it is incident from the lens end of the fiber collimator and emitted from the pigtail end of the fiber collimator. The pigtail of the fiber collimator used in the embodiment of the present invention is a PM 1550 optical fiber.

[0043] The spectrum broadening fiber 4 is used to make the seed pulse output by the seed laser 1 undergo nonlinear spectrum broadening and generate spectrum sideband components outside the central wavelength; the spectrum broadening amount of the nonlinear spectrum broadening is regulated by the adjustment amount of the energy regulator 2, the type and length of the spectrum broadening fiber 4. The spectrum broadening fiber 4 used in the embodiment of the present invention is PM 1550 fiber with a length of 2m. The spectrum broadening fiber 4 is connected to the fiber collimator pigtail by fiber fusion splicing.

[0044] The first fiber coupler 5 is a 2×2 fiber coupler with a splitting ratio of 20 / 80 and a PM 1550 fiber. The seed laser enters the coupler from one of the incident ends and is emitted from the 20% output end and enters the mode-locked oscillator. The seed laser spectrum at this time is as follows: Figure 2 As shown, it can be seen that about 20nm spectrum broadening sidebands are formed on both sides of the 1533.6nm main wavelength peak signal.

[0045] The first filter 6 and the second filter 12 are bandpass filters with bandwidths in the nm range; the central wavelength of the first filter 6 is adjustable in the range of at least 1545-1549nm or 1551-1555nm, and the bandpass frequency band of the first filter 6 does not include the central wavelength of the seed pulse before spectrum broadening, so that the seed pulse retains only a small amount of spectral sideband components after passing through the first filter 6. In the embodiment of the present invention, the first filter 6 is a bandpass filter with a bandwidth of approximately 8nm, and the central wavelength is adjustable in the range of 1540-1550nm; the second filter 12 is a bandpass filter with a bandwidth of approximately 2nm, and the central wavelength is 1550nm. Preferably, the central wavelength of the first filter 6 is adjusted to 1542nm. Figure 2 , the seed pulse laser will filter out the main wavelength components and irrelevant spectrum sideband components that occupy most of the time when passing through the first filter 6, and only retain the spectrum sidebands within the range of 1542±4nm. These spectrum sideband components will participate in the subsequent mode-locked start-up process of the mode-locked oscillator as real seed pulses, achieving efficient start-up and stable operation of the mode-locked oscillator.

[0046] The isolator 7 is a fiber isolator, which is used to ensure that the laser (including the seed pulse laser and the mode-locked oscillation) operates unidirectionally in the all-fiber ring resonator.

[0047] The first pump source 8 outputs pump light which is incident into the mode-locked oscillator through the first wavelength division multiplexer 9; the second pump source 13 outputs pump light which is incident into the mode-locked oscillator through the second wavelength division multiplexer 14; the first pump source 8 and the second pump source 13 output pump light in the 980nm band or the 1480nm band. In the embodiment of the present invention, the first pump source 8 and the second pump source 13 output pump light in the 980nm band, the maximum pump power is 0.8W, the output optical fiber is PM 980, and they are respectively incident through the PM 980 ends of the first wavelength division multiplexer 9 and the second wavelength division multiplexer 14.

[0048] The first erbium-doped optical fiber 10 and the second erbium-doped optical fiber 15 are polarization-maintaining optical fibers that exhibit normal dispersion characteristics in at least the range of 1540 to 1560 nm. Preferably, the polarization-maintaining optical fiber used is RightWave EDF07PM SR, and the length of each is 10 m.

[0049] The second optical fiber coupler is a 1×2 optical fiber coupler. Preferably, the splitting ratio is 20 / 80, wherein the 80% end is used as laser output.

[0050] The operating wavelength of other unspecified devices is 1550nm, and the pigtails are PM 1550.

[0051] When the laser is working for the first time, the first pump source 8 and the second pump source 13 need to output pump light of a certain power to excite the gain medium in the erbium-doped fiber. The first filter 6 and the second filter 12 should minimize the overlap of the passband frequency band to form the necessary conditions of the Mamyshev mechanism. The seed pulse energy and spectrum broadening are adjusted by controlling the energy regulator 2 to start mode locking. When the intracavity parameters such as the laser pump power and the filter passband frequency band are fixed, the mode locking can be started by starting the seed pulse injection.

[0052] Figure 3 The figure is a diagram of the mode-locked pulse sequence output by the laser in this embodiment, with a repetition frequency of 5.15MHz. By adjusting the pump power, the output mode-locked pulse energy can also be changed. In this embodiment, a mode-locked pulse output with a maximum energy of 15nJ can be obtained. The spectrum of the mode-locked output of the laser at different pulse energies is shown in FIG. Figure 4 shown.

[0053] Those skilled in the art will appreciate that the modules in the devices in the embodiments of the present invention may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments of the present invention may be combined into one module or unit or component, and in addition they may be divided into a plurality of submodules or subunits or subcomponents. Except that at least some of such features and / or processes or units are mutually exclusive, all features disclosed in this specification (including corresponding claims, abstracts and drawings) and all processes or units of any method or device disclosed in this manner may be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including corresponding claims, abstracts and drawings) may be replaced by an alternative feature providing the same, equivalent or similar purpose.

[0054] Through the description of the above implementation methods, technical personnel in the relevant field can understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0055] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0056] In addition, the terms "first", "second", etc. used in the embodiments of the present invention are only used for descriptive purposes and should not be understood as indicating or implying relative importance, or implicitly indicating the number of technical features indicated in the present embodiment. Therefore, the features defined by the terms "first", "second", etc. in the embodiments of the present invention can explicitly or implicitly indicate that the embodiment includes at least one of the features. In the description of the present invention, the word "multiple" means at least two or two or more, such as two, three, four, etc., unless otherwise clearly and specifically defined in the embodiments.

[0057] In the embodiments of the present invention, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element. In addition, components, features, and elements with the same name in different embodiments of the present invention may have the same meaning or different meanings, and their specific meanings need to be determined by their explanation in the specific embodiment or further combined with the context in the specific embodiment.

[0058] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and cannot be construed as limitations of the present invention, and those of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention. Those skilled in the art will readily come to think of other embodiments of the present invention after considering the specification and practicing the present invention. This application is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common knowledge or customary technical means in the art that are not disclosed in the present invention. The specification and embodiments are intended to be exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

Claims

1. A seed injection-started erbium-doped fiber mode-locked laser, characterized in that: include: A seed laser (1), an energy regulator (2), a space-fiber coupler (3), a spectrum broadening fiber (4), a first fiber coupler (5), a first filter (6), an isolator (7), a first pump source (8), a first wavelength division multiplexer (9), a first erbium-doped fiber (10), a second fiber coupler (11), a second filter (12), a second pump source (13), a second wavelength division multiplexer (14), and a second erbium-doped fiber (15); The seed laser (1), the energy regulator (2), the space-fiber coupler (3), the spectrum-broadening fiber (4), the first fiber coupler (5) and the first filter (6) are connected in sequence to form a seed injection start-up device; in the seed injection start-up device, the seed pulse emitted by the seed laser is used to start the mode-locked laser after being spectrum-broadened by the spectrum-broadening fiber (4) and spectrum-filtered by the first filter (6); The first optical fiber coupler (5), the first filter (6), the isolator (7), the first wavelength division multiplexer (9), the first erbium-doped optical fiber (10), the second optical fiber coupler (11), the second filter (12), the second wavelength division multiplexer (14) and the second erbium-doped optical fiber (15) are connected in sequence by optical fiber fusion splicing to form an all-fiber ring resonator; the all-fiber ring resonator and the first pump source (8) and the second pump source (13) form a mode-locked oscillator; and mode-locked pulse output is achieved through the mode-locked oscillator.

2. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: In the seed injection start-up device, the seed pulse output by the seed laser (1) has the following characteristics: The central wavelength is within the range of 1530-1540nm or 1560-1570nm; The pulse width is between 1 and 100 ns; The peak power is greater than 1kW.

3. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The energy regulator (2) is used to regulate the energy of the seed pulse output by the seed laser (1); the energy regulation accuracy of the energy regulator is not less than 5% of the original energy of the seed pulse.

4. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The space-fiber coupler (3) is used to shrink the seed pulse output by the seed laser (1), limit the light spot of the seed pulse to a size comparable to the diameter of the optical fiber core, and inject it into the spectrum broadening optical fiber (4).

5. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The spectrum broadening optical fiber (4) is used to cause nonlinear spectrum broadening of the seed pulse output by the seed laser (1) and to generate spectrum sideband components outside the central wavelength; the spectrum broadening amount of the nonlinear spectrum broadening is regulated by the adjustment amount of the energy regulator (2) and the type and length of the spectrum broadening optical fiber (4).

6. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The seed pulse output by the seed laser (1) is incident through an input end of the first optical fiber coupler (5) and enters the mode-locked oscillator.

7. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The first filter (6) and the second filter (12) are bandpass filters with bandwidths in the order of nm; the central wavelength of the first filter (6) is adjustable at least within the range of 1545 to 1549 nm or 1551 to 1555 nm, and the bandpass frequency band of the first filter (6) does not include the central wavelength of the seed pulse before spectrum broadening, so that the seed pulse retains only a small amount of spectrum sideband components after passing through the first filter (6).

8. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The first pump source (8) outputs pump light which is incident on the mode-locked oscillator through the first wavelength division multiplexer (9); the second pump source (13) outputs pump light which is incident on the mode-locked oscillator through the second wavelength division multiplexer (14); The first pump source (8) and the second pump source (13) output pump light in the 980 nm band or the 1480 nm band.

9. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The first erbium-doped optical fiber (10) and the second erbium-doped optical fiber (15) are polarization-maintaining optical fibers that exhibit normal dispersion characteristics in a range of at least 1540 to 1560 nm.

10. The seed injection-started erbium-doped fiber mode-locked laser according to claim 1, characterized in that: The operating frequency band of the first optical fiber coupler (5), the isolator (7), the first wavelength division multiplexer (9), the first erbium-doped optical fiber (10), the second optical fiber coupler (11), the second filter (12), the second wavelength division multiplexer (14) and the second erbium-doped optical fiber (15) is 1550 nm.

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