A bidirectional mode-locked fiber laser

Abstract

The application discloses a bidirectional mode-locked fiber laser, which comprises clockwise and counterclockwise lasers, forward and reverse erbium-doped optical fibers, six circulators and a mode-locked element; wherein the clockwise laser emits light which is injected into the forward erbium-doped optical fiber, transmitted through the first, second and third circulators, reflected by the mode-locked element, transmitted through the third, fourth and fifth circulators and returned to the forward erbium-doped optical fiber, and then amplified in the forward erbium-doped optical fiber to form clockwise mode-locked pulses; the counterclockwise laser emits light which is injected into the reverse erbium-doped optical fiber, transmitted through the fifth, fourth and sixth circulators, reflected by the mode-locked element, transmitted through the sixth, second and first circulators and returned to the reverse erbium-doped optical fiber, and then amplified in the reverse erbium-doped optical fiber to form counterclockwise mode-locked pulses. The bidirectional mode-locked fiber laser can realize independent control and adjustment of forward and reverse pulses and can increase the controllable range.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a bidirectional mode-locked fiber laser. Background Technology

[0002] A dual-frequency comb consists of two optical frequency combs with slightly different repetition frequencies. One comb serves as the signal light, and the other as the local light. The two interact, and an interference waveform is extracted in the time domain. When building a dual-frequency comb structure based on two independent mode-locked lasers, a complex frequency-locked electronic feedback control system is required to strictly lock the repetition frequency and the carrier envelope phase shift frequency to reference frequencies such as atomic clocks. This results in a complex structure and high cost, making it difficult to use on a large scale.

[0003] A dual-comb mode-locked fiber laser is a type of laser that uses polarization multiplexing, spatial multiplexing, directional multiplexing, and wavelength multiplexing to generate two lasers through the same laser resonator. The use of directional multiplexing mode-locked fiber lasers can effectively simplify the system and save costs.

[0004] Current directional multiplexing structures mainly use a single-fiber bidirectional pumping structure to generate clockwise and counterclockwise pulses, which has problems such as difficulty in adjusting output power and the inability to independently adjust the spectrum of the two pulses.

[0005] Current dual-comb mode-locked fiber lasers that use saturable absorber Bragg mirrors as saturable absorbers mainly achieve dual-comb output by passing through two identical saturable absorber Bragg mirrors, which results in weak output pulse coherence.

[0006] Existing technical solutions mainly employ two 980 lasers to pump the same erbium-doped fiber to amplify forward and reverse pulses. As shown in the figure below, 1 and 7 represent 980 lasers, 2 and 6 represent 980 isolators mainly used to prevent the bidirectional pumping 980 light from damaging the lasers, and 4 represents the erbium-doped fiber. Due to the slight difference in forward and reverse gain of the erbium-doped fiber, under conditions of intracavity polarization and matching forward and reverse pump power, two pulses can exist simultaneously in the cavity, with a slight difference in pulse repetition frequency.

[0007] Because the existing technology uses the method of bidirectional pumping the same erbium-doped fiber to achieve forward and reverse pulses that cannot be adjusted independently; and because the method of bidirectional pumping the same erbium-doped fiber to achieve forward and reverse pulses results in the polarization state inside the cavity, the bidirectional pumping power ratio has strict requirements, the adjustable range is small, and the results of repeated activation are inconsistent. Summary of the Invention

[0008] In view of this, the purpose of this invention is to propose a bidirectional mode-locked fiber laser that enables independent control and adjustment of forward and reverse pulses, and can increase the controllable range.

[0009] To achieve the above objectives, the present invention provides a bidirectional mode-locked fiber laser, comprising: a clockwise and a counterclockwise laser, erbium-doped fibers in the forward and reverse directions, six circulators, and a mode-locking element;

[0010] In this process, the light emitted by the clockwise laser is injected into the forward erbium-doped fiber, transmitted through the first, second, and third circulators, reflected by the mode-locking element, transmitted through the third, fourth, and fifth circulators, and returned to the forward erbium-doped fiber. The light is then amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse.

[0011] The light emitted by the counterclockwise laser is injected into the reverse erbium-doped fiber, transmitted through the fifth, fourth, and sixth circulators, reflected by the mode-locking element, and then transmitted back to the reverse erbium-doped fiber through the sixth, second, and first circulators. The light is then cyclically amplified by the reverse erbium-doped fiber to form a counterclockwise mode-locked pulse.

[0012] Preferably, the light emitted by the clockwise laser is injected into the forward erbium-doped fiber, specifically through port 1 of the first circulator and output from port 2; the light output from port 2 of the first circulator is injected through port 2 of the second circulator and output from port 3; the light output from port 3 of the second circulator is injected through port 1 of the third circulator and output from port 2; the light output from port 2 of the third circulator, after being reflected by the mode-locking element, is injected through port 2 of the third circulator and output from port 3; the light output from port 3 of the third circulator is injected through port 1 of the fourth circulator and output from port 2; the light output from port 2 of the fourth circulator is injected through port 2 of the fifth circulator and output from port 3; the light output from port 3 of the fifth circulator is cyclically amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse.

[0013] Preferably, the light emitted by the clockwise laser is injected into the forward erbium-doped fiber, specifically through port 1 of the first circulator and output from port 2; the light output from port 2 of the first circulator is injected through port 2 of the second circulator and output from port 3; the light output from port 3 of the second circulator is injected through port 1 of the third circulator and output from port 2; the light output from port 2 of the third circulator, after being reflected by the mode-locking element, is injected through port 2 of the third circulator and output from port 3; the light output from port 3 of the third circulator is injected through port 1 of the fourth circulator and output from port 2; the light output from port 2 of the fourth circulator is injected through port 2 of the fifth circulator and output from port 3; the light output from port 3 of the fifth circulator is cyclically amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse.

[0014] Furthermore, the bidirectional mode-locked fiber laser also includes: a coupler disposed between port 2 of the first circulator and port 2 of the second circulator, and forward and reverse isolators;

[0015] Wherein, the light output from port 2 of the first circulator passes through the coupler, part of which is emitted through the forward isolator and the other part enters the second circulator;

[0016] The light output from port 2 of the second circulator passes through the coupler, and part of it is emitted through the reverse isolator, while the other part enters the first circulator.

[0017] Preferably, the mode-locking element is specifically a single semiconductor saturable absorber mirror; and

[0018] Port 2 of the third circulator and port 2 of the sixth circulator are respectively connected to the third optical fiber through the first and second optical fibers, and then connected to the semiconductor saturable absorber mirror through the third optical fiber.

[0019] Preferably, a polarization beam splitter is also provided between the third optical fiber and the semiconductor saturable absorber mirror.

[0020] Furthermore, the bidirectional mode-locked fiber laser further includes: a reverse light filter disposed between port 2 of the third circulator and the first fiber; and

[0021] A forward optical filter is installed between port 2 of the sixth circulator and the second optical fiber.

[0022] The bidirectional mode-locked fiber laser provided in this embodiment of the invention includes: clockwise and counterclockwise lasers, forward and reverse erbium-doped fibers, six circulators, and a mode-locking element. The light emitted by the clockwise laser is injected into the forward erbium-doped fiber, transmitted through the first, second, and third circulators, reflected by the mode-locking element, and then transmitted through the third, fourth, and fifth circulators before returning to the forward erbium-doped fiber. The light is then amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse. Similarly, the light emitted by the counterclockwise laser is injected into the reverse erbium-doped fiber, transmitted through the fifth, fourth, and sixth circulators, reflected by the mode-locking element, and then transmitted through the sixth, second, and first circulators before returning to the reverse erbium-doped fiber. The light is then amplified by the reverse erbium-doped fiber to form a counterclockwise mode-locked pulse.

[0023] In this structure, clockwise and counterclockwise pulses are separated by a circulator and then generated by a mode-locking element. This allows for easy design of the repetition rate difference between the clockwise and counterclockwise pulses, achieving a repetition rate difference of 1Hz to over 10MHz. Furthermore, by using a circulator to separate the clockwise and counterclockwise pulses for independent amplification and control, the repetition rate difference and spectrum of the forward and reverse pulses can be independently controlled and adjusted. In addition, using erbium-doped fiber for amplification of the clockwise and counterclockwise pulses also facilitates independent adjustment of the clockwise and counterclockwise output optical pulses. The output power of the clockwise and counterclockwise pulses is independently controlled by the clockwise 980nm laser and the counterclockwise 980nm laser, thus expanding the controllable range.

[0024] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention also includes a polarization beam splitter. Clockwise and counterclockwise pulses are coupled to a semiconductor saturable absorber mirror via the polarization beam splitter, achieving high polarization isolation in both clockwise and counterclockwise directions. Return light, after passing through the polarization beam splitter, remains in a single polarization state and is aligned to the slow axis. This improves the system's anti-interference capability. The use of a circulator combination with the polarization beam splitter achieves near-unidirectional transmission of forward and reverse pulses, avoiding the problem in bidirectional mode-locked lasers where reflective mode-locking devices cannot transmit pulses bidirectionally. Moreover, the polarization beam splitter used in the bidirectional mode-locked fiber laser provided by this invention replaces the circulator in the prior art semiconductor saturable absorber mirror scheme, achieving bidirectional pulse polarization coupling and possessing high polarization isolation.

[0025] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a semiconductor saturable absorber mirror as the mode-locking element, which can achieve good self-starting performance, locks upon power-on without complex adjustment, and has high spectral consistency across multiple power-on and power-off cycles.

[0026] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a single semiconductor saturable absorber mirror as a mode-locking element, which can effectively improve the coherence of pulses in both clockwise and counterclockwise directions.

[0027] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a polarization beam splitter and a single semiconductor saturable absorber mirror to generate forward and reverse mode-locked pulses, resulting in a simple structure. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of a bidirectional mode-locked fiber laser in the prior art.

[0030] Figure 2 This is a schematic diagram of a bidirectional mode-locked fiber laser provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0032] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0033] The bidirectional mode-locked fiber laser provided by this invention includes: clockwise and counterclockwise lasers, forward and reverse erbium-doped fibers, six circulators, and a mode-locking element. The light emitted by the clockwise laser is injected into the forward erbium-doped fiber, transmitted through the first, second, and third circulators, reflected by the mode-locking element, and then transmitted through the third, fourth, and fifth circulators before returning to the forward erbium-doped fiber. The light is then amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse. Similarly, the light emitted by the counterclockwise laser is injected into the reverse erbium-doped fiber, transmitted through the fifth, fourth, and sixth circulators, reflected by the mode-locking element, and then transmitted through the sixth, second, and first circulators before returning to the reverse erbium-doped fiber. The light is then amplified by the reverse erbium-doped fiber to form a counterclockwise mode-locked pulse.

[0034] In this structure, clockwise and counterclockwise pulses are separated by a circulator and then output via a mode-locking element. This allows for easy design of the repetition rate difference between the clockwise and counterclockwise pulses, achieving a repetition rate difference of 1Hz to over 10MHz. Furthermore, the circulator separates the clockwise and counterclockwise pulses for independent amplification and control, enabling independent control and adjustment of the repetition rate difference and spectrum between the forward and reverse pulses. Additionally, using erbium-doped fiber for amplification of the clockwise and counterclockwise pulses further facilitates independent adjustment of the clockwise and counterclockwise output optical pulses. The output power of the clockwise and counterclockwise pulses is independently controlled by the clockwise 980nm laser and the counterclockwise 980nm laser, thus expanding the controllable range.

[0035] Furthermore, the bidirectional mode-locked fiber laser provided by this invention also includes a polarization beam splitter. Clockwise and counterclockwise pulses are coupled to a semiconductor saturable absorber mirror via the polarization beam splitter, achieving high polarization isolation in both clockwise and counterclockwise directions. Return light, after passing through the polarization beam splitter, remains in a single polarization state and is aligned to the slow axis. This improves the system's anti-interference capability. The use of a circulator combination with the polarization beam splitter achieves near-unidirectional transmission of forward and reverse pulses, avoiding the problem in bidirectional mode-locked fiber lasers where the mode-locking device cannot transmit pulses bidirectionally. Moreover, the polarization beam splitter used in the bidirectional mode-locked fiber laser provided by this invention replaces the circulator in the prior art semiconductor saturable absorber mirror scheme, achieving bidirectional pulse polarization coupling and possessing high polarization isolation.

[0036] Furthermore, the bidirectional mode-locked fiber laser provided by this invention uses a semiconductor saturable absorber mirror as the mode-locking element, which can achieve good self-starting performance, locks immediately upon power-on without complex adjustment, and has high spectral consistency across multiple power-on and power-off cycles.

[0037] Furthermore, the bidirectional mode-locked fiber laser provided by this invention uses a single semiconductor saturable absorber mirror as a mode-locking element, which can effectively improve the coherence of pulses in both clockwise and counterclockwise directions.

[0038] Furthermore, the bidirectional mode-locked fiber laser provided by this invention uses a polarization beam splitter and a single semiconductor saturable absorber mirror to generate forward and reverse mode-locked pulses, resulting in a simple structure.

[0039] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] This invention provides a bidirectional mode-locked fiber laser, the structure of which is as follows: Figure 2 As shown, it includes: a clockwise laser 7, a counterclockwise laser 1, a forward erbium-doped fiber 9, a reverse erbium-doped fiber 3, six circulators, and a mode-locking element.

[0041] The six circulators are specifically the first circulator 4, the second circulator 16, the third circulator 13, the fourth circulator 12, the fifth circulator 10, and the sixth circulator 11.

[0042] Specifically, the light emitted by the clockwise laser 7 is injected into the forward erbium-doped fiber 9 and then output from port 2 through port 1 of the first circulator 4; the light output from port 2 of the first circulator 4 is injected into port 3 through port 2 of the second circulator 16; the light output from port 3 of the second circulator 16 is injected into port 2 through port 1 of the third circulator 13; the light output from port 2 of the third circulator 13, after being reflected by the mode-locking element, is injected into port 3 through port 2 of the third circulator 13; the light output from port 3 of the third circulator 13 is injected into port 2 through port 1 of the fourth circulator 12; the light output from port 2 of the fourth circulator 12 is injected into port 3 through port 2 of the fifth circulator 10; and the light output from port 3 of the fifth circulator 10 is amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse.

[0043] The light emitted by the counterclockwise laser 1 is injected into the reverse erbium-doped fiber 3 and then output from port 2 through port 1 of the fifth circulator 10. The light output from port 2 of the fifth circulator 10 is injected into port 3 through port 2 of the fourth circulator 12. The light output from port 3 of the fourth circulator 12 is injected into port 2 through port 1 of the sixth circulator 11. The light output from port 2 of the sixth circulator 11, after being reflected by the mode-locking element, is injected into port 3 through port 2 of the sixth circulator 11. The light output from port 3 of the sixth circulator 11 is injected into port 2 through port 1 of the second circulator 16. The light output from port 2 of the second circulator 16 is injected into port 3 through port 2 of the first circulator 4. The light output from port 3 of the first circulator 4 is cyclically amplified by the reverse erbium-doped fiber to form a counterclockwise mode-locked pulse.

[0044] Because the aforementioned structure uses a circulator to separate the clockwise and counterclockwise pulses before achieving mode-locked pulse output via a mode-locking element, it is easy to design the repetition rate difference between the clockwise and counterclockwise pulses, achieving a repetition rate difference of 1Hz to over 10MHz. Furthermore, by using a circulator to separate the clockwise and counterclockwise pulses for independent amplification and control, that is, by using a circulator to separate the forward and reverse pulses, independent control and adjustment of the repetition rate difference and spectrum between the forward and reverse pulses can be achieved. In addition, using erbium-doped fiber for amplification of the clockwise and counterclockwise pulses also helps to achieve independent adjustment of the clockwise and counterclockwise output optical pulses. The output power of the clockwise and counterclockwise pulses is independently controlled by the clockwise 980nm laser and the counterclockwise 980nm laser, thus expanding the controllable range.

[0045] Specifically, the forward wavelength division multiplexer 8 is positioned between the clockwise laser 7 and the forward erbium-doped fiber 9. The clockwise 980nm laser 7 acts as a clockwise pump, injecting light into the forward erbium-doped fiber 9 through the forward 980nm / 1550nm wavelength division multiplexer 8.

[0046] The reverse wavelength division multiplexer 2 is positioned between the counterclockwise laser 1 and the reverse erbium-doped fiber 3. The counterclockwise 980nm laser 1 acts as a counterclockwise pump, injecting light into the reverse erbium-doped fiber 3 through the reverse 980nm / 1550nm wavelength division multiplexer 2.

[0047] The aforementioned clockwise and counterclockwise 980nm lasers can be replaced by a 980nm coupler with a high-power 980nm laser.

[0048] Coupler 6 is disposed between port 2 of the first circulator 4 and port 2 of the second circulator 16;

[0049] The forward light output from port 2 of the first circulator 4 passes through a coupler 6 with a coupling ratio of 50:50, with 50% of the light being output as output light. This output light passes through port 3 of the coupler 6 and is then output through the forward isolator 17. The remaining 50% of the light passes through port 4 of the coupler 6 and is injected into port 3 of the second circulator 16 via port 2.

[0050] The reverse light output from port 2 of the second circulator 16 passes through coupler 6 with a coupling ratio of 50:50, with 50% of the light being output as output light. It then passes through port 2 of coupler 6 and is output via reverse isolator 5. The remaining 50% of the light passes through port 1 of coupler 6, through port 2 of the first circulator 4, and is injected into port 3.

[0051] The aforementioned mode-locking element may specifically be a nonlinear annular mirror or a component based on nonlinear polarization rotation technology. Preferably, the aforementioned mode-locking element may specifically include two semiconductor saturable absorber mirrors, respectively connected to port 2 of the sixth circulator and port 2 of the third circulator.

[0052] More preferably, the aforementioned mode-locking element is specifically a single semiconductor saturable absorber mirror 15; and

[0053] Port 2 of the third circulator 13 and port 2 of the sixth circulator 11 are respectively connected to the third optical fiber through the first and second optical fibers, and then connected to the semiconductor saturable absorber mirror 15 through the third optical fiber.

[0054] More preferably, port 2 of the third circulator 13 and port 2 of the sixth circulator 11 are respectively connected to one end of the polarization beam splitter 14 through the first and second optical fibers. The other end of the polarization beam splitter 14 is connected to the third optical fiber and then connected to the semiconductor saturable absorber mirror 15 through the third optical fiber.

[0055] Using a semiconductor saturable absorber mirror as the mode-locking element, it can achieve good self-starting performance, locks immediately upon power-on without complex adjustments, and has high spectral consistency across multiple power-on and power-off cycles.

[0056] Using a single semiconductor saturable absorber mirror as a mode-locking element can effectively improve the coherence of clockwise and counterclockwise pulses.

[0057] Clockwise and counterclockwise pulses are coupled to a semiconductor saturable absorber mirror via a polarization beamsplitter, achieving high polarization isolation in both directions. Returning light, after passing through the polarization beamsplitter, remains single-polarized and aligned to the slow axis. This improves the system's anti-interference capability.

[0058] The polarization beam splitter can be replaced by a 45-degree angle fusion splice of polarization-maintaining fiber. After the replacement, the pulse polarization isolation in the clockwise and counterclockwise directions decreases, but the mode-locked pulse output in the clockwise and counterclockwise directions can still be achieved.

[0059] More preferably, the forward optical filter 19 is disposed between port 2 of the sixth circulator 11 and the second optical fiber; the reverse optical filter 18 is disposed between port 2 of the third circulator 13 and the first optical fiber.

[0060] The forward / reverse optical filter can be implemented using a birefringence filter or a comb filter scheme.

[0061] The bidirectional mode-locked fiber laser provided in this embodiment of the invention includes: clockwise and counterclockwise lasers, forward and reverse erbium-doped fibers, six circulators, and a mode-locking element. The light emitted by the clockwise laser is injected into the forward erbium-doped fiber, transmitted through the first, second, and third circulators, reflected by the mode-locking element, and then transmitted through the third, fourth, and fifth circulators before returning to the forward erbium-doped fiber. The light is then amplified by the forward erbium-doped fiber to form a clockwise mode-locked pulse. Similarly, the light emitted by the counterclockwise laser is injected into the reverse erbium-doped fiber, transmitted through the fifth, fourth, and sixth circulators, reflected by the mode-locking element, and then transmitted through the sixth, second, and first circulators before returning to the reverse erbium-doped fiber. The light is then amplified by the reverse erbium-doped fiber to form a counterclockwise mode-locked pulse.

[0062] In this structure, clockwise and counterclockwise pulses are separated by a circulator and then output via a mode-locking element. This allows for easy design of the repetition rate difference between the clockwise and counterclockwise pulses, achieving a repetition rate difference of 1Hz to over 10MHz. Furthermore, the circulator separates the clockwise and counterclockwise pulses for independent amplification and control, enabling independent control and adjustment of the repetition rate difference and spectrum between the forward and reverse pulses. Additionally, using erbium-doped fiber for amplification of the clockwise and counterclockwise pulses further facilitates independent adjustment of the clockwise and counterclockwise output optical pulses. The output power of the clockwise and counterclockwise pulses is independently controlled by the clockwise 980nm laser and the counterclockwise 980nm laser, thus expanding the controllable range.

[0063] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention also includes a polarization beam splitter. Clockwise and counterclockwise pulses are coupled to the semiconductor saturable absorber mirror through the polarization beam splitter, achieving high polarization isolation in both clockwise and counterclockwise directions. Return light, after passing through the polarization beam splitter, remains in a single polarization state and is aligned to the slow axis. This improves the system's anti-interference capability. The use of a circulator combination with the polarization beam splitter achieves near-unidirectional transmission of forward and reverse pulses, avoiding the problem in bidirectional mode-locked fiber lasers where the mode-locking device cannot transmit pulses bidirectionally. Moreover, the polarization beam splitter used in the bidirectional mode-locked fiber laser provided by this invention replaces the circulator in the prior art semiconductor saturable absorber mirror scheme, achieving bidirectional pulse polarization coupling and possessing high polarization isolation.

[0064] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a semiconductor saturable absorber mirror as the mode-locking element, which can achieve good self-starting performance, locks upon power-on without complex adjustment, and has high spectral consistency across multiple power-on and power-off cycles.

[0065] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a single semiconductor saturable absorber mirror as a mode-locking element, which can effectively improve the coherence of pulses in both clockwise and counterclockwise directions.

[0066] Furthermore, the bidirectional mode-locked fiber laser provided in this embodiment of the invention uses a polarization beam splitter and a single semiconductor saturable absorber mirror to generate forward and reverse mode-locked pulses, resulting in a simple structure.

[0067] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0068] The embodiments of this invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A bidirectional mode-locked fiber laser, comprising: clockwise and counterclockwise lasers, forward and backward doped erbium fibers, six circulators, and a mode-locked element; The light emitted by the clockwise laser is injected into the forward doped erbium fiber, and then injected into port 1 of the first circulator through port 2 of the first circulator and output from port 2 of the first circulator; the light output from port 2 of the first circulator is injected into port 2 of the second circulator through port 2 of the second circulator and output from port 3 of the second circulator; the light output from port 3 of the second circulator is injected into port 1 of the third circulator through port 1 of the third circulator and output from port 2 of the third circulator; The light output from port 2 of the third circulator is injected into port 2 of the third circulator through port 2 of the third circulator after being reflected by the mode-locked element, and output from port 3 of the third circulator; the light output from port 3 of the third circulator is injected into port 1 of the fourth circulator through port 1 of the fourth circulator and output from port 2 of the fourth circulator; the light output from port 2 of the fourth circulator is injected into port 2 of the fifth circulator through port 2 of the fifth circulator and output from port 3 of the fifth circulator; the light output from port 3 of the fifth circulator is circulated and amplified by the forward doped erbium fiber to form clockwise mode-locked pulses; The light emitted by the counterclockwise laser is injected into the backward doped erbium fiber, and then injected into port 1 of the fifth circulator through port 1 of the fifth circulator and output from port 2 of the fifth circulator; the light output from port 2 of the fifth circulator is injected into port 2 of the fourth circulator through port 2 of the fourth circulator and output from port 3 of the fourth circulator; the light output from port 3 of the fourth circulator is injected into port 1 of the sixth circulator through port 1 of the sixth circulator and output from port 2 of the sixth circulator; The light output from port 2 of the sixth circulator is injected into port 2 of the sixth circulator through port 2 of the sixth circulator after being reflected by the mode-locked element, and output from port 3 of the sixth circulator; the light output from port 3 of the sixth circulator is injected into port 1 of the second circulator through port 1 of the second circulator and output from port 2 of the second circulator; the light output from port 2 of the second circulator is injected into port 2 of the first circulator through port 2 of the first circulator and output from port 3 of the first circulator; the light output from port 3 of the first circulator is circulated and amplified by the backward doped erbium fiber to form counterclockwise mode-locked pulses.

2. The bidirectional mode-locked fiber laser of claim 1, wherein, Further comprising: a coupler arranged between port 2 of the first circulator and port 2 of the second circulator, and forward and backward isolators; The light output from port 2 of the first circulator passes through the coupler, part of which is emitted through the forward isolator, and the other part enters the second circulator; The light output from port 2 of the second circulator passes through the coupler, part of which is emitted through the backward isolator, and the other part enters the first circulator.

3. The bidirectional mode-locked fiber laser according to claim 1 or 2, characterized in that, The mode-locked element specifically includes two semiconductor saturable absorption mirrors, respectively connected to port 2 of the sixth circulator and port 2 of the third circulator.

4. The bidirectional mode-locked fiber laser of claim 1 or 2, wherein, The mode-locked element specifically includes a single semiconductor saturable absorption mirror; and Port 2 of the third circulator and port 2 of the sixth circulator are respectively connected to the third optical fiber through the first and second optical fibers, and then connected to the semiconductor saturable absorption mirror through the third optical fiber.

5. The bidirectional mode-locked fiber laser of claim 4, wherein, A polarization beam splitter is further arranged between the third optical fiber and the semiconductor saturable absorption mirror.

6. The bidirectional mode-locked fiber laser of claim 5, wherein, Further comprising: a backward optical filter arranged between port 2 of the third circulator and the first optical fiber; and a forward optical filter arranged between port 2 of the sixth circulator and the second optical fiber.

7. The bidirectional mode-locked fiber laser of claim 1, wherein, The mode-locked element is specifically a nonlinear ring mirror, or an element of nonlinear polarization rotation technology.

8. The bidirectional mode-locked fiber laser of claim 1 or 2, wherein, Further comprising: a forward wavelength division multiplexer disposed between the clockwise laser and the forward doped erbium fiber; and a backward wavelength division multiplexer disposed between the counterclockwise laser and the backward doped erbium fiber.

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