A seed-injection-started erbium-doped fiber mode-locked laser

Abstract

The present invention discloses an erbium-doped fiber mode-locked laser with seed injection startup. A seed laser, an energy regulator, a spatial fiber coupler, a spectrum-broadening fiber, a first fiber coupler, and a first filter are sequentially connected to form a seed injection startup device. The first fiber coupler, a first filter, an isolator, a first wavelength division multiplexer, a first erbium-doped fiber, a second fiber coupler, a second filter, a second wavelength division multiplexer, and a second erbium-doped fiber are sequentially connected by fiber fusion to form an all-fiber ring resonator. The all-fiber ring resonator, together with the first and second pump sources, form a mode-locked oscillator. Mode-locked pulse output is achieved through the mode-locked oscillator. The present invention achieves low-cost, efficient, and reliable passive mode-locked startup and high-energy ultrafast pulse generation by regulating and injecting nanosecond pulses emitted by the seed laser into the mode-locked laser.

Description

Technical Field

[0001] The present 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, bioimaging, 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 makes it difficult for the mode-locked state to start 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 to start the mode-locked operation by introducing external picosecond (ps)-level ultrafast laser pulses.

[0003] However, the external light sources that provide these ultrafast pulses (such as gain-switched laser diodes or mode-locked lasers) are often complex and expensive, which poses a challenge to practical applications. Currently, 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. However, 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 traditional seed injection-started Mamyshev mechanism erbium-doped fiber mode-locked lasers, thereby achieving low-cost seed injection start-up and high-performance ultrashort pulse generation in the 1550nm band.

[0005] A 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 starting device; in the seed injection starting 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 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 connected in sequence by 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 starting 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] Pulse width is between 1 and 100 ns;

[0011] 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 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).

[0014] Furthermore, the spectrum-broadening optical fiber (4) is used to cause the seed pulse output by the seed laser (1) to 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) 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 via 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 a bandwidth 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 980nm band or the 1480nm band.

[0019] Furthermore, the first erbium-doped optical fiber (10) and the second erbium-doped optical fiber (15) are polarization-maintaining optical fibers exhibiting 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] Embodiments of the present invention have the following beneficial effects: A seed-injection-initiated erbium-doped fiber mode-locked laser utilizes a seed laser with a nanosecond (ns) pulse width. By controlling the spectral broadening of the seed pulse and filtering out the useless components that account for the majority of the energy, low-cost, stable, and reliable seed-injection-initiated mode-locking is achieved. By constructing an all-fiber ring Mamyshev oscillator cavity, the present invention enables stable, high-performance ultrafast pulse generation. Furthermore, by sharing a fiber coupler and filter with the seed-injection-initiating device, the laser structure is simplified.

[0022] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by 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 following briefly introduces the drawings required for use in the description of the embodiments. 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 any creative work.

[0024] Figure 1 The figure 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-locked 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 by 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall 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 spatial-fiber coupler 3, the spectrum-stretching fiber 4, the first fiber coupler 5, and the first filter 6 are sequentially connected to form a seed injection and starting device. In the seed injection and starting device, the seed pulse emitted by the seed laser is used to start the mode-locked laser after being spectrum-stretched by the spectrum-stretching fiber 4 and spectrum-filtered by the first filter 6.

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

[0033] The Mamyshev mechanism is a passive mode-locking technique used in mode-locked lasers. This technique locks multiple longitudinal modes of light together, causing them to overlap in time and interfere with each other to form ultrashort pulses. The Mamyshev mechanism utilizes the self-phase modulation (SPM) and spectral filtering effects of light 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. By connecting the 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 center wavelength of the filter, it has a strong ability to suppress continuous noise, thereby ensuring 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 center 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 achieve mode-locked pulse output of the Mamyshev mechanism.

[0036] Specifically, in the seed injection startup 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] Pulse width is between 1 and 100 ns;

[0039] 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. It outputs seed pulse lasers with a central wavelength of 1533.6 nm, a bandwidth of less than 0.2 nm, a pulse energy of 120 μJ, a pulse width of approximately 4 ns, a peak power of approximately 30 kW, and a repetition rate adjustable from 1 to 20 Hz. In addition to the Er glass laser mentioned in the embodiment of the present invention, seed lasers such as a gain-switched laser diode + power amplifier laser and a passively Q-switched fiber laser can also be used to output seed pulse lasers.

[0041] Energy regulator 2 is used to adjust the energy of the seed pulse output by seed laser 1. The energy regulator's energy regulation accuracy is no less than 5% of the original seed pulse energy. For example, when the seed pulse energy is 120 μJ, the regulation accuracy is ≤ 6 μJ, achieving high-precision energy regulation. In an embodiment of the present invention, energy regulator 2 comprises a half-wave plate and a polarization beam splitter cube. Rotating the half-wave plate allows for continuous adjustment of the laser energy of the seed pulse output by the seed laser, thereby controlling the spectral broadening during subsequent fiber propagation. Alternatively, a graded neutral density filter can be used as the energy regulator.

[0042] The space-fiber coupler 3 is used to beam-contract the seed pulse output by the seed laser 1, limiting the seed pulse spot size to a size comparable to the fiber core diameter, and injecting it into the spectrum-broadening fiber 4. In this embodiment of the present invention, the space-fiber coupler 3 consists of a plano-convex lens (focal length f = 200 mm) and a fiber collimator. The plano-convex lens collimates the output laser light from the seed laser 1, which is then incident on the lens end of the fiber collimator and emitted from the pigtail end of the fiber collimator. The pigtail used in the fiber collimator in this embodiment of the present invention is a PM 1550 fiber.

[0043] Spectrum-stretching fiber 4 is used to nonlinearly broaden the seed pulses output by seed laser 1, generating spectral sideband components outside the central wavelength. The amount of nonlinear spectrum broadening is controlled by the adjustment of energy modulator 2 and the type and length of spectrum-stretching fiber 4. The spectrum-stretching fiber 4 used in this embodiment of the present invention is PM 1550 fiber with a length of 2 meters. Spectrum-stretching fiber 4 is connected to the fiber collimator pigtail using 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 pigtail. The seed laser enters the coupler from one of the input ports and exits from the 20% output port into the mode-locked oscillator. The seed laser spectrum at this time is as follows: Figure 2 As shown in FIG. 1 , it can be seen that spectrum broadening sidebands of about 20 nm are formed on both sides of the 1533.6 nm main wavelength peak signal.

[0045] The first filter 6 and the second filter 12 are bandpass filters with a bandwidth in the nm range; the center 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 center 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 an embodiment of the present invention, the first filter 6 is a bandpass filter with a bandwidth of about 8nm, and the center wavelength is adjustable in the range of 1540-1550nm; the second filter 12 is a bandpass filter with a bandwidth of about 2nm, and the center wavelength is 1550nm. Preferably, the center wavelength of the first filter 6 is adjusted to 1542nm. Combined Figure 2 When the seed pulse laser passes through the first filter 6, most of the main wavelength components and irrelevant spectral sideband components are filtered out, leaving only the spectral sidebands within the range of 1542±4nm. These spectral sideband components will serve as the true seed pulses and participate in the subsequent mode-locked startup process of the mode-locked oscillator, achieving efficient startup 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 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 pump light output by the first pump source 8 and the second pump source 13 is in the 980nm band or the 1480nm band. In this embodiment of the present invention, the first pump source 8 and the second pump source 13 output pump light in the 980nm band, with a maximum pump power of 0.8W. The output fiber is PM 980, and is incident on the PM 980 ports of the first wavelength division multiplexer 9 and the second wavelength division multiplexer 14, respectively.

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

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

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

[0051] During initial laser operation, the first and second pump sources 8 and 13 must output pump light of a certain power to excite the gain medium in the erbium-doped fiber. The first and second filters 6 and 12 must minimize the overlap of their passbands to establish the necessary conditions for the Mamyshev mechanism. The energy regulator 2 is used to adjust the seed pulse energy and spectral broadening to initiate mode locking. When the laser's intracavity parameters, such as pump power and filter passbands, are fixed, mode locking can be initiated simply by injecting the seed pulse.

[0052] Figure 3 The following 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 laser mode-locked output at different pulse energies is shown in Figure 1. Figure 4 shown.

[0053] Those skilled in the art will appreciate that the modules in the devices in the embodiments of the present invention can be adaptively changed and set in one or more devices different from the embodiments. The modules or units or components in the embodiments of the present invention can be combined into one module or unit or component, and in addition they can be divided into multiple sub-modules or sub-units or sub-components. 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 can be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including corresponding claims, abstracts and drawings) can be replaced by an alternative feature that provides 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 distributed and completed by 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] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0056] In addition, the terms "first" and "second" 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 this embodiment. Therefore, the features defined by the terms "first" and "second" in the embodiments of the present invention can explicitly or implicitly indicate that the embodiment includes at least one of such features. In the description of the present invention, the word "plurality" 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 "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus comprising 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 apparatus. In the absence of further restrictions, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or apparatus comprising 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 of the specific embodiment.

[0058] Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and are not to 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 appreciate 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 examples are intended to be exemplary only, and the true scope and spirit of the present invention are indicated by the claims below.

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 starting device; in the seed injection starting 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 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 connected in sequence by 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 starting 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; Pulse width is between 1 and 100 ns; 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 the seed pulse output by the seed laser (1) to 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) 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 via 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 within a range of at least 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 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); The first pump source (8) and the second pump source (13) output pump light at a wavelength of 980 nm or 1480 nm.

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 exhibiting 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 wavelength 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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