High repetition frequency all-fiber passive mode-locked laser

Abstract

The invention belongs to the technical field of lasers, and particularly relates to a high repetition frequency all-fiber passive mode-locked laser, which is characterized in that a composite wavelength division multiplexer and a semiconductor saturable absorber mirror form a laser resonant cavity, a pumping source provides pumping energy through the composite wavelength division multiplexer, and a gain fiber completes population inversion. And finally, mode locking is realized by the semiconductor saturable absorption mirror. The whole structure is simple, the number of devices in the cavity is small, and stable high-repetition-frequency mode-locked pulse output can be achieved in a relatively simple and convenient mode; while the overall cost is reduced, passive mode-locking pulse light output with high repetition frequency can be obtained more easily; the implementation difficulty is lower, the process is simpler, the operation difficulty can be effectively reduced in industrial application, and the technology feasibility is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lasers, and particularly relates to a high-repetition-rate all-fiber passively mode-locked laser. BACKGROUND

[0002] Passively mode-locked fiber lasers have excellent thermal management capability, power scalability, and outstanding environmental stability and system integration, and have been widely used in precision machining and manufacturing, biomedical imaging and treatment, communication and information processing, and frontier scientific research in recent years. As a key device for mode locking, the semiconductor saturable absorber mirror has stable self-starting mode locking capability, low insertion loss, high integration, customizable parameters, and wide wavelength adaptability, and becomes the preferred device for mode locking.

[0003] High-repetition-rate pulsed light (especially pulsed light with a repetition rate of 80 MHz or more) has great application potential in distributed fiber sensing systems, terahertz communication systems, quantum entangled photon sources, and high-resolution spectroscopy due to its high time resolution and strong noise suppression capability. However, in passively mode-locked fiber lasers, the repetition rate is limited by the physical constraints of the number of fiber devices and the minimum fusion length. The current mainstream solution is to use a fiber grating and a semiconductor saturable absorber mirror as the two ends of the resonant cavity, and move the wavelength division multiplexer outside the cavity to shorten the cavity length, but this solution requires a higher manufacturing process for the fiber grating and significantly increases the overall cost of the laser. SUMMARY

[0004] The purpose of the present application is to provide a high-repetition-rate all-fiber passively mode-locked laser to solve the above problems.

[0005] To achieve the above purpose, the present application provides the following solutions:

[0006] A high-repetition-rate all-fiber passively mode-locked laser comprises a pump source, the output tail fiber of the pump source is connected to the reflection end of a composite wavelength division multiplexer, one end of the gain fiber is connected to the common end of the composite wavelength division multiplexer, the semiconductor saturable absorber mirror is coupled to the other end of the gain fiber, the transmission end of the composite wavelength division multiplexer is used for laser emission, and the composite wavelength division multiplexer and the semiconductor saturable absorber mirror form a laser resonant cavity.

[0007] In the high-repetition-rate all-fiber passively mode-locked laser of the present application, the end of the gain fiber away from the composite wavelength division multiplexer is connected to a fiber focusing device, and the fiber focusing device is coupled to the semiconductor saturable absorber mirror.

[0008] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the composite wavelength division multiplexer comprises a first double-fiber collimator, a first self-focusing reflective lens, a single-fiber reflective lens and a chirped Bragg fiber grating arranged in sequence, and the first double-fiber collimator is connected with the output pigtail of the pump source and the gain fiber.

[0009] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the composite wavelength division multiplexer comprises a first double-fiber collimator, a first self-focusing reflective lens, a single-fiber reflective lens and a chirped Bragg fiber grating arranged in sequence, and the first double-fiber collimator is connected with the output pigtail of the pump source and the gain fiber.

[0010] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the pump source comprises a fiber output laser with a center wavelength of 976 nm.

[0011] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the length of the gain fiber is 0.1 m-1 m.

[0012] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the length of the laser resonant cavity is 0.2 m-10 m.

[0013] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the gain fiber is an active fiber, and the gain fiber is doped with at least one of ytterbium, erbium, thulium and bismuth.

[0014] Compared with the prior art, the application has the following advantages and technical effects:

[0015] In the high-repetition-rate all-fiber passively mode-locked laser of the application, the composite wavelength division multiplexer comprises a first double-fiber collimator, a first self-focusing reflective lens, a single-fiber reflective lens and a chirped Bragg fiber grating arranged in sequence, and the first double-fiber collimator is connected with the output pigtail of the pump source and the gain fiber.

[0016] The application has the advantages of simple overall structure, small number of in-cavity devices, and stable high-repetition-rate mode-locked pulse output in a relatively simple manner. Compared with the traditional scheme of using a fiber grating and a semiconductor saturable absorber mirror as the two ends of the resonant cavity and moving the wavelength division multiplexer outside the cavity, the application has a simpler structure, reduces the overall cost, and is easier to obtain high-repetition-rate passively mode-locked pulse light output. Compared with the high-repetition-rate passively mode-locked fiber laser scheme relying on complex composite devices or fine cavity process, the application has lower structure implementation difficulty and simpler process, which can effectively reduce the operation difficulty and improve the technical implementability in industrial applications. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0018] Fig. 1 It is a schematic diagram of the overall structure of the present application.

[0019] Fig. 2 It is a schematic diagram of the structure of the composite wavelength division multiplexer in Embodiment 1.

[0020] Fig. 3 It is a schematic diagram of the structure of the composite wavelength division multiplexer in Embodiment 2.

[0021] 1, pump source; 2, composite wavelength division multiplexer; 3, gain optical fiber; 4, optical fiber focusing device; 5, semiconductor saturable absorber mirror; 6, composite structure; 201, second double-fiber collimator; 202, second self-focusing reflective lens; 203, light splitting mirror; 204, single-fiber collimator; 2001, first double-fiber collimator; 2002, first self-focusing reflective lens; 2003, single-fiber reflective lens; 2004, chirped Bragg fiber grating. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort fall within the scope of the present application.

[0023] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0024] Embodiment 1

[0025] Referring to Figs. 1-2 The present embodiment discloses a high-repetition-rate all-fiber passive mode-locked laser, comprising: a pump source 1, an output tail fiber of the pump source 1 is connected with a reflective end of a composite wavelength division multiplexer 2, a common end of the composite wavelength division multiplexer 2 is connected with one end of a gain optical fiber 3, the other end of the gain optical fiber 3 is coupled with a semiconductor saturable absorber mirror 5, a transmission end of the composite wavelength division multiplexer 2 is used for laser emission, and a laser resonant cavity is formed between the composite wavelength division multiplexer 2 and the semiconductor saturable absorber mirror 5.

[0026] The reflection end of the composite wavelength division multiplexer 2 has a reflection effect on the pump light of a specific wavelength band; the common end of the composite wavelength division multiplexer has a partial reflection effect on the signal light of a specific wavelength band; and the output end of the composite wavelength division multiplexer has a partial transmission effect on the signal light of a specific wavelength band, and the transmission rate is 1% to 10%.

[0027] In an alternative solution, the gain fiber 3 is connected with a fiber focus 4 at one end away from the composite wavelength division multiplexer 2, and the fiber focus 4 is coupled with the semiconductor saturable absorber mirror 5.

[0028] The pump source 1 and the gain fiber 3 are connected by fusion splicing through the reflection end and the common end of the composite wavelength division multiplexer 2, and the gain fiber 3 and the fiber focus 4 are connected by fusion splicing, and there is no passive optical fiber between them.

[0029] The fiber focus 4 and the semiconductor saturable absorber mirror 5 are coupled and packaged as a composite structure 6.

[0030] The packaging mode of the semiconductor saturable absorber mirror 5 and the fiber focus 4 includes but is not limited to: packaging by pasting the semiconductor saturable absorber mirror 5 to the end face of the fiber jumper, coupling and relatively fixing the fiber focus 4 and the semiconductor saturable absorber mirror 5, and packaging by fixing the semiconductor saturable absorber mirror 5 to the heat sink and fixing with the flange and the fiber jumper.

[0031] In an alternative solution, the composite wavelength division multiplexer 2 includes a first double-fiber collimator 2001, a first self-focusing reflection lens 2002, a single-fiber reflection lens 2003, and a chirped Bragg fiber grating 2004 arranged in sequence, the first double-fiber collimator 2001, the first self-focusing reflection lens 2002, the single-fiber reflection lens 2003, and the chirped Bragg fiber grating 2004 are coupled, and the first double-fiber collimator 2001 is connected with the output tail fiber of the pump source 1 and the gain fiber 3.

[0032] The first self-focusing reflection lens 2002 and the single-fiber reflection lens 2003 are integrated in the composite wavelength division multiplexer 2, so that the composite wavelength division multiplexer 2 has a reflection effect on the laser, in which case a laser resonant cavity is formed between the composite wavelength division multiplexer 2 and the semiconductor saturable absorber mirror 5, the pump source 1 provides pump energy through the composite wavelength division multiplexer 2, the gain fiber 3 completes particle inversion, and finally the semiconductor saturable absorber mirror 5 realizes mode locking.

[0033] The function of the chirped Bragg fiber grating 2004 is to make the composite wavelength division multiplexer 2 have a dispersion management function.

[0034] In an alternative solution, the pump source 1 includes a fiber output laser with a center wavelength of 976 nm.

[0035] The pump source 1 is connected to the circuit control system of the constant temperature module to ensure that the constant temperature stable pumping effect can be achieved when the ambient temperature changes and the pump source 1 itself temperature changes.

[0036] In an alternative, the length of the gain fiber 3 is 0.1m-1m.

[0037] In an alternative, the length of the laser resonant cavity is 0.2m-10m.

[0038] The length of the laser resonant cavity is 0.2m-10m, corresponding to the pulse repetition frequency of 10-500MHz that can be output by the high repetition rate passively mode-locked fiber laser.

[0039] In an alternative, the gain fiber 3 is an active fiber, and the gain fiber 3 is doped with at least one of ytterbium, erbium, thulium and bismuth.

[0040] Specifically, the gain fiber 3 doped with erbium is selected, and fiber types with different symbol dispersion amounts are used to cooperate with the overall dispersion to achieve dispersion management.

[0041] One example is as follows:

[0042] A high repetition rate all-fiber passively mode-locked laser includes a pump source 1, an output tail fiber of the pump source 1 is connected with a reflection end of a composite wave division multiplexer 2, a common end of the composite wave division multiplexer 2 is connected with a gain fiber 3, the gain fiber 3 is connected with a fiber focus 4, the fiber focus 4 is coupled with a semiconductor saturable absorber mirror 5, and the fiber focus 4 and the semiconductor saturable absorber mirror 5 are coupled and packaged.

[0043] The composite wave division multiplexer performs 1%-10% light splitting and 90%-99% reflection on signal light from the common end to the transmission end, and performs ≥90% reflection on pump light from the common end to the transmission end.

[0044] In operation, the area between the composite wave division multiplexer 2 and the semiconductor saturable absorber mirror 5 is a resonant cavity, the pump light of the pump source 1 is coupled into the laser cavity under the action of the composite wave division multiplexer 2, the driving current of the pump source is increased to make the gain generated by the pump power greater than the cavity loss, so that the laser resonant cavity is oscillated.

[0045] The pump light obtains gain every time it passes through the gain fiber 3 in the resonant cavity, and the saturable absorption effect occurs when it passes through the semiconductor saturable absorber mirror 5, so that the signal light with strong light intensity is reflected back, and the signal light with weak light intensity is absorbed by the semiconductor saturable absorber mirror 5, thereby narrowing the pulse width and achieving the effect of mode locking.

[0046] The signal light forms a pulse in the resonant cavity, and then is output through the transmission end of the compound wave division multiplexer 2. The tail fiber length of the common end of the compound wave division multiplexer 2 and the length of the gain optical fiber 3 can be adjusted to realize the adjustment of the repetition frequency, and the gain optical fiber 3 can be replaced by a gain optical fiber type with a higher rare earth ion doping concentration to realize the effect of shorter cavity length and higher repetition frequency.

[0047] In order to control the cavity dispersion, the compound wave division multiplexer 2 is provided with a chirped Bragg fiber grating 2004, so that the compound wave division multiplexer 2 can flexibly control the cavity dispersion, and the system is further integrated. In this scheme, the compound wave division multiplexer 2 includes a first double-fiber collimator 2001, a first self-focusing reflective lens 2002, a single-fiber reflective lens 2003 and a chirped Bragg fiber grating 2004. The chirped Bragg fiber grating 2004 is used to provide dispersion management and reflection and transmission functions of the signal light.

[0048] Embodiment 2

[0049] Reference Fig. 3 The difference between the embodiment 1 and the embodiment 2 is that the compound wave division multiplexer 2 uses a reflective film to realize the reflection and output of the signal light. In this scheme, the compound wave division multiplexer 2 includes a second double-fiber collimator 201, a second self-focusing reflective lens 202, a beam splitter 203 and a single-fiber collimator 204 arranged in sequence. The double-fiber collimator 201 is connected with the output tail fiber of the pump source 1 and the gain optical fiber 3.

[0050] In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0051] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A high-repetition-rate all-fiber passively mode-locked laser, characterized in that, The application relates to a laser device. The gain optical fiber (3) is connected with a fiber focusing device (4) at one end away from the composite wave division multiplexer (2), and the fiber focusing device (4) is coupled with the semiconductor saturable absorber mirror (5).

2. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: The composite wave division multiplexer (2) comprises a first double-fiber collimator (2001), a first self-focusing reflection lens (2002), a single-fiber reflection lens (2003) and a chirped Bragg fiber grating (2004) arranged in sequence, and the first double-fiber collimator (2001), the first self-focusing reflection lens (2002), the single-fiber reflection lens (2003) and the chirped Bragg fiber grating (2004) are coupled.

3. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: The composite wave division multiplexer (2) comprises a second double-fiber collimator (201), a second self-focusing reflection lens (202), a light splitting reflection mirror (203) and a single-fiber collimator (204) arranged in sequence, and the second double-fiber collimator (201), the second self-focusing reflection lens (202), the light splitting reflection mirror (203) and the single-fiber collimator (204) are coupled. ​ 4. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: The pump source (1) comprises a fiber output laser with a center wavelength of 976 nm.

5. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: The length of the gain optical fiber (3) is 0.1 m-1 m.

6. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: The length of the laser resonant cavity is 0.2 m-10 m.

7. A high-repetition-rate all-fiber passively mode-locked laser according to claim 1, characterized in that: The gain optical fiber (3) is an active optical fiber, and at least one of ytterbium, erbium, thulium and bismuth is doped in the gain optical fiber (3).

8. The high-repetition-rate all-fiber passively mode-locked laser of claim 1, wherein: ​

Images