An ultrashort resonant cavity high repetition rate fiber laser with adjustable repetition rate

Abstract

The present invention discloses a high-repetition-rate fiber laser with an ultrashort resonant cavity and adjustable repetition rate. The laser comprises a pump source, a wavelength division multiplexer (WDM), an optical isolator, and an ultrashort resonant cavity with adjustable repetition rate. The WDM couples pump light generated by the pump source into the ultrashort resonant cavity with adjustable repetition rate and outputs the generated signal light outside the ultrashort resonant cavity. The optical isolator is connected to the WDM. The ultrashort resonant cavity with adjustable repetition rate comprises a first gradient-index lens, a second gradient-index lens, a ferrule, a sleeve, a gain fiber, a semiconductor saturable absorber mirror, and a dielectric film. The present invention achieves high-repetition-rate passively mode-locked laser pulse output with adjustable repetition rate by adjusting the distance between the first and second gradient-index lenses to change the cavity length of the ultrashort resonant cavity.

Description

Technical Field

[0001] The invention belongs to the field of high repetition rate passively mode-locked fiber lasers, and in particular relates to an ultrashort resonant cavity high repetition rate fiber laser with adjustable repetition frequency. Background Art

[0002] High-repetition-rate laser sources hold significant research value and application potential in numerous fields, including precision spectral measurement, high-speed optical sampling, high-quality optical communications, precision micromachining, and nonlinear bioimaging. Furthermore, compared to solid-state lasers, semiconductor lasers, gas lasers, and dye lasers, fiber lasers offer significant advantages, such as compact structure, low manufacturing cost, strong heat dissipation, and high pump conversion efficiency. These advantages have made them highly sought after in scientific research and industrial processing, making them the preferred choice for research into high-reliability, high-pulse-quality laser sources.

[0003] Mode locking is an important means of generating femtosecond ultrashort pulses, and passively mode-locked fiber lasers are the primary method for generating high-repetition-rate ultrashort pulses. To enhance the practical application of passively mode-locked lasers, researchers have attempted to improve laser performance in multiple dimensions, such as achieving shorter pulse widths, higher output power, lower intensity noise, and adjustable output wavelength. To meet the needs of diverse scenarios and applications, it is particularly important to achieve adjustable output laser pulse repetition rates by using a single laser to achieve multiple repetition rates.

[0004] According to the laser repetition frequency formula It can be seen that in order to achieve adjustable repetition rate, the length of the resonant cavity can be changed. In 2004, BR Washburn et al. achieved repetition rate adjustment from 49.3 MHz to 50.1 MHz by adding a fiber delay line to an erbium-doped fiber ring cavity, with a repetition rate change of 800 kHz (Washburn B, Fox R, Newbury N, et al. Fiber-laser-based frequency comb with a tunable repetition rate [J]. Optics Express, 2004, 12 (20): 4999-5004.). For high repetition rate fiber lasers, the repetition rate of its fundamental frequency > 1 GHz means that its resonant cavity length will be limited to the cm level. Therefore, a cavity length change of mm will bring about a repetition rate change of MHz or even GHz. For high repetition rate lasers that are ultrashort resonant cavities, it is difficult to achieve a small change in the resonant cavity by using traditional fiber delay lines. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide an ultrashort cavity high-repetition rate fiber laser with adjustable repetition rate based on a gradient refractive index lens. Two gradient refractive index lenses are added to the ultrashort cavity. The distance between the first gradient refractive index lens and the second gradient refractive index lens is changed to change the cavity length of the ultrashort cavity, so as to achieve adjustable repetition rate of laser pulse output by the high-repetition rate fiber laser.

[0006] In order to achieve the above object, the present invention is implemented by at least one of the following technical solutions:

[0007] A high-repetition-rate fiber laser with an ultrashort resonant cavity and adjustable repetition frequency comprises: a pump source, a wavelength division multiplexer, an optical isolator, and an ultrashort resonant cavity with adjustable repetition frequency. The wavelength division multiplexer is used to couple pump light generated by the pump source into the ultrashort resonant cavity with adjustable repetition frequency and output the generated signal light outside the ultrashort resonant cavity with adjustable repetition frequency. The optical isolator is connected to the wavelength division multiplexer.

[0008] Furthermore, the ultrashort resonant cavity with adjustable repetition frequency comprises: a first gradient refractive index lens, a second gradient refractive index lens, a ferrule, a sleeve, a gain fiber, a semiconductor saturable absorber mirror and a dielectric film;

[0009] The semiconductor saturable absorber mirror is arranged on one end face of the first gradient refractive index lens, the other end of the first gradient refractive index lens is spaced apart and connected to one end of the second gradient refractive index lens through a sleeve, the other end of the second gradient refractive index lens is connected to one end of the ferrule, a dielectric film is arranged on the other end face of the ferrule, and the gain optical fiber is located in the ferrule.

[0010] Furthermore, the ultrashort resonant cavity with adjustable repetition frequency comprises: a first gradient refractive index lens, a second gradient refractive index lens, a ferrule, a sleeve, a gain fiber, a semiconductor saturable absorber mirror and a dielectric film;

[0011] The semiconductor saturable absorber mirror is arranged on one end face of the ferrule, the other end of the ferrule is connected to one end of the first gradient refractive index lens, the other end of the first gradient refractive index lens is spaced apart and connected to one end of the second gradient refractive index lens through a sleeve, a dielectric film is arranged on the other end face of the second gradient refractive index lens, and the gain fiber is located in the ferrule.

[0012] Furthermore, the sleeve is arranged outside the first ferrule, the first gradient refractive index lens and the second gradient refractive index lens.

[0013] Furthermore, the ultrashort resonant cavity with adjustable repetition frequency includes: a first gradient index lens, a second gradient index lens, a first ferrule, a second ferrule, a first sleeve, a second sleeve, a third sleeve, a first gain fiber, a second gain fiber, a semiconductor saturable absorber mirror, and a dielectric film;

[0014] The semiconductor saturable absorber mirror is arranged on one end face of the first ferrule, the other end of the first ferrule is connected to one end of the first gradient index lens through the second sleeve, the second gradient index lens is connected to the second ferrule through the third sleeve, the dielectric film is arranged on the end face of the second ferrule, the other end of the first gradient index lens is connected to the second gradient index lens at an interval through the first sleeve, the first gain fiber is located in the first ferrule, and the second gain fiber is located in the second ferrule.

[0015] Furthermore, parallel light is transmitted between the first gradient refractive index lens and the second gradient refractive index lens. Changing the distance between the first gradient refractive index lens and the second gradient refractive index lens will not affect the propagation trajectory of the parallel light therebetween. That is, by adjusting the distance L1 between the first gradient refractive index lens and the second gradient refractive index lens, the total cavity length L of the ultrashort resonant cavity can be adjusted.

[0016] Furthermore, the ultrashort resonant cavity with adjustable repetition frequency is a Fabry-Perot cavity.

[0017] Furthermore, the reflectivity of the dielectric film to the generated laser light is greater than 60%.

[0018] Furthermore, the modulation depth of the semiconductor saturable absorption mirror is 1% to 10%.

[0019] Furthermore, the gain fiber is a rare earth ion doped fiber, and the doped rare earth ions include one or more of erbium, ytterbium, thulium and holmium.

[0020] Furthermore, the cavity length of the ultrashort resonant cavity with adjustable repetition frequency is 1 to 10 centimeters.

[0021] Furthermore, the pump source is a semiconductor single-mode laser.

[0022] Compared with the existing technology, the beneficial effects of the present invention are:

[0023] The present invention uses two gradient refractive index lenses in an ultrashort resonant cavity. By changing the distance between the first gradient refractive index lens and the second gradient refractive index lens, the total cavity length of the ultrashort resonant cavity can be adjusted, thereby changing the repetition frequency of the output pulses of a high repetition rate laser. This meets the different needs of people in various application scenarios when using high repetition rate lasers, minimizes economic and time costs, and maximizes the efficiency of resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly describes the drawings required for use in the embodiments. It should be understood that the following drawings illustrate only certain embodiments of the present invention and should not be construed as limiting the scope of the present invention. Those skilled in the art can, without inventive effort, derive other relevant drawings from these drawings.

[0025] Figure 1 This is a schematic diagram of the structure of the ultrashort resonant cavity high repetition rate fiber laser with adjustable repetition rate provided by the present invention;

[0026] Figure 2 A schematic diagram of the structure of an ultrashort resonant cavity with adjustable repetition frequency provided in Example 1 of the present invention;

[0027] Figure 3 A schematic diagram of the structure of an ultrashort resonant cavity with adjustable repetition frequency provided in Example 2 of the present invention;

[0028] Figure 4 This is a schematic diagram of the ultrashort resonant cavity structure with adjustable repetition frequency provided in Example 3 of the present invention. 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 the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation examples. It should be noted that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

[0031] Example 1

[0032] like Figure 1 As shown, this embodiment provides a high-repetition-rate fiber laser with an ultrashort resonant cavity and adjustable repetition rate, comprising a pump source 3, a wavelength division multiplexer 2, an optical isolator 4, and an ultrashort resonant cavity 1 with adjustable repetition rate. The wavelength division multiplexer 2 is used to couple the pump light generated by the pump source 3 into the ultrashort resonant cavity 1 with adjustable repetition rate and output the generated signal light to the outside of the ultrashort resonant cavity 1 with adjustable repetition rate. The optical isolator 4 is connected to the wavelength division multiplexer 2 to prevent the influence of return light.

[0033] like Figure 2As shown, the repetition frequency adjustable ultrashort resonant cavity 1 comprises: a first gradient refractive index lens 6, a second gradient refractive index lens 8, a ferrule 10, a sleeve 7, a gain fiber 9, a semiconductor saturable absorber mirror 5 and a dielectric film 11;

[0034] The semiconductor saturable absorber mirror 5 is arranged on one end face of the first gradient refractive index lens 6. The other end of the first gradient refractive index lens 6 is connected to one end of the second gradient refractive index lens 8 via a sleeve 7. The other end of the second gradient refractive index lens 8 is connected to one end of the ferrule 10. A dielectric film 11 is provided on the other end face of the ferrule 10. The sleeve 7 is arranged on the outside of the ferrule 10, the first gradient refractive index lens 6, and the second gradient refractive index lens 8.

[0035] In practical applications, the ultrashort resonant cavity is a Fabry-Perot cavity structure with a compact resonant cavity structure and an overall length of <10 cm. It can achieve a repetition rate of >1 GHz and a repetition rate adjustment of MHz or even GHz.

[0036] The pump source 3 is a semiconductor single-mode laser with a central wavelength of 974 nm and a maximum pump power of 460 mW.

[0037] The dielectric film 7 is a dichroic dielectric film deposited on one end face of the ferrule 10 by plasma sputtering, and has a high transmittance (>80%) for pump light and a high reflectivity (>80%) for signal light.

[0038] The semiconductor saturable absorber mirror 5 is fixed on one end face of the first gradient refractive index lens 2. Its central wavelength is 1040nm, the area is 1×1mm, the thickness is 450μm, the modulation depth is 5%, the unsaturated loss is 3%, and the saturation flux is 40μJ / cm 2 , relaxation time is 1ps, damage threshold is 3mJ / cm 2 .

[0039] The gain fiber 9 is fixed in the ferrule 10 using optical glue and is an ytterbium rare earth ion doped fiber.

[0040] The ferrule 10 is a ceramic ferrule with an inner diameter of 125 μm, which matches the cladding diameter of the gain fiber 9 , and an outer diameter of 2.5 mm, which is equal to the outer diameters of the first gradient index lens 6 and the second gradient index lens 8 . Both ends of the ferrule 10 need to be vertically polished.

[0041] The sleeve 7 is a ceramic sleeve with an inner diameter of 2.5 mm, which matches the outer diameters of the ferrule 10 , the first gradient index lens 6 and the second gradient index lens 8 .

[0042] The first gradient index lens 6 and the second gradient index lens 8 affect the optical path by changing the refractive index of the lens itself. The refractive index changes with the radial direction. All the optical paths in the lens are the same. It can convert parallel light and light transmitted in the optical fiber. Therefore, parallel light is transmitted between the first gradient index lens 6 and the second gradient index lens 8. Changing the distance between the two gradient index lenses will not change the propagation trajectory of light between them. By changing the distance L1 between the two gradient index lenses, the length L of the entire ultrashort resonant cavity can be changed. It can be seen that changing the cavity length of the ultrashort resonant cavity can adjust the laser repetition frequency. When the distance between the two gradient refractive index lenses changes by ΔL1, the laser repetition frequency changes by (the cavity length becomes longer) or (The cavity length becomes shorter).

[0043] Example 2

[0044] like Figure 3 As shown, the ultrashort resonant cavity 1 with adjustable repetition frequency provided in this embodiment includes: a first gradient index lens 6, a second gradient index lens 8, a ferrule 10, a sleeve 7, a gain fiber 9, a semiconductor saturable absorber mirror 5 and a dielectric film 11.

[0045] The ultrashort resonant cavity 1 with adjustable repetition frequency provided in this embodiment differs from that in Example 1 in that the semiconductor saturable absorber mirror 5 is disposed on one end face of a ferrule 10, the other end of the ferrule 10 is connected to one end of a first gradient index lens 6, the other end of the first gradient index lens 6 is spaced apart and connected to one end of a second gradient index lens 8 via a sleeve 7, and a dielectric film 11 is disposed on the other end face of the second gradient index lens 8.

[0046] In practical applications, the pump source 3 is a semiconductor single-mode laser with a central wavelength of 976 nm and a maximum pump power of 480 mW.

[0047] The dielectric film 7 is a dichroic dielectric film deposited on one end surface of the second gradient index lens 8 by plasma sputtering, and has a high transmittance (>80%) for pump light and a high reflectivity (>80%) for signal light.

[0048] The semiconductor saturable absorber mirror 5 is fixed on one end face of the first gradient refractive index lens 2. Its central wavelength is 1550nm, the area is 1×1mm, the thickness is 450μm, the modulation depth is 4%, the unsaturated loss is 6%, and the saturation flux is 15μJ / cm 2 , relaxation time is 5ps, damage threshold is 1mJ / cm 2 .

[0049] The gain fiber 9 is fixed in the ferrule 10 using optical glue and is an erbium-ytterbium co-doped rare earth ion doped fiber.

[0050] Example 3

[0051] like Figure 4 As shown, the ultrashort resonant cavity 1 with adjustable repetition frequency provided in this embodiment includes: a first gradient index lens 6, a second gradient index lens 8, a first ferrule 10, a second ferrule 14, a first sleeve 7, a second sleeve 12, a third sleeve 13, a first gain fiber 9, a second gain fiber 15, a semiconductor saturable absorber mirror 5 and a dielectric film 11;

[0052] The ultrashort resonant cavity 1 with adjustable repetition frequency provided in this embodiment differs from that in Example 1 in that the semiconductor saturable absorber mirror 5 is disposed on one end face of a first ferrule 10, the other end of the first ferrule 10 is connected to one end of a first gradient index lens 6 via a second sleeve 12, the second gradient index lens 8 is connected to a second ferrule 14 via a third sleeve 13, the dielectric film 11 is disposed on an end face of the second ferrule 14, and the other end of the first gradient index lens 6 is connected to the second gradient index lens 8 via a first sleeve 7.

[0053] In practical applications, the pump source 3 is a semiconductor single-mode laser with a central wavelength of 1570 nm and a maximum pump power of 500 mW.

[0054] The dielectric film 7 is a dichroic dielectric film deposited on one end of the second ferrule 14 by plasma sputtering, and has a high transmittance (>80%) for pump light and a high reflectivity (>80%) for signal light.

[0055] The semiconductor saturable absorber mirror 5 is fixed on one end face of the first ferrule 10. Its central wavelength is 2000nm, the area is 1×1mm, the thickness is 450μm, the modulation depth is 12%, the unsaturated loss is 8%, and the saturation flux is 65μJ / cm 2 , relaxation time is 10ps, damage threshold is 2mJ / cm 2 .

[0056] The first gain fiber 9 and the second gain fiber 15 are fixed in the first ferrule 10 and the second ferrule 14 respectively using optical glue, and are thulium rare earth ion doped fibers.

[0057] The first ferrule 10 and the second ferrule 14 are both ceramic ferrules with an inner diameter of 125 μm, which matches the cladding diameter of the first gain fiber 9 and the second gain fiber 15. The outer diameter is 2.5 mm, which is equal to the outer diameter of the first gradient refractive index lens 6 and the second gradient refractive index lens 8. Both ends of the first ferrule 10 and the second ferrule 14 need to be vertically polished.

[0058] The first sleeve 7 , the second sleeve 12 and the third sleeve 13 are all ceramic sleeves with an inner diameter of 2.5 mm, which matches the outer diameters of the first ferrule 10 , the second ferrule 14 , the first gradient index lens 6 and the second gradient index lens 8 .

[0059] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0060] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. An ultrashort cavity high repetition rate fiber laser with adjustable repetition rate, characterized in that: include: A pump source (3), a wavelength division multiplexer (2), an optical isolator (4), and an ultrashort resonant cavity (1) with adjustable repetition frequency, wherein the wavelength division multiplexer (2) is used to couple pump light generated by the pump source (3) into the ultrashort resonant cavity (1) with adjustable repetition frequency and output the generated signal light to the outside of the ultrashort resonant cavity (1) with adjustable repetition frequency, and the optical isolator (4) is connected to the wavelength division multiplexer (2); The repetition frequency adjustable ultrashort resonant cavity (1) comprises: a first gradient refractive index lens (6), a second gradient refractive index lens (8), a core (10), a sleeve (7), a gain optical fiber (9), a semiconductor saturable absorber mirror (5) and a dielectric film (11); The semiconductor saturable absorber mirror (5) is arranged on one end face of the first gradient refractive index lens (6), the other end of the first gradient refractive index lens (6) is spaced apart and connected to one end of the second gradient refractive index lens (8) through a sleeve (7), the other end of the second gradient refractive index lens (8) is connected to one end of the ferrule (10), and a dielectric film (11) is arranged on the other end face of the ferrule (10), and the gain optical fiber (9) is located in the ferrule (10); the ferrule (10) is a ceramic ferrule with an inner diameter of 125 μm, which matches the cladding diameter of the gain optical fiber (9), and an outer diameter of 2.5 mm, which is equal to the outer diameters of the first gradient refractive index lens (6) and the second gradient refractive index lens (8), and both ends of the ferrule (10) need to be vertically polished; the sleeve (7) is a ceramic sleeve with an inner diameter of 2.5 mm, which matches the outer diameters of the ferrule (10), the first gradient refractive index lens (6) and the second gradient refractive index lens (8); Parallel light is transmitted between the first gradient refractive index lens (6) and the second gradient refractive index lens (8), and changing the distance between the first gradient refractive index lens (6) and the second gradient refractive index lens (8) will not affect the propagation trajectory of the parallel light therebetween, that is, by adjusting the distance L1 between the first gradient refractive index lens (6) and the second gradient refractive index lens (8), the total cavity length L of the ultrashort resonant cavity (1) is adjusted. The ultrashort resonant cavity (1) is a Fabry-Perot cavity structure, the resonant cavity structure is compact, and the overall length of the structure is less than 10 cm.

2. The ultrashort cavity high repetition rate fiber laser with adjustable repetition rate according to claim 1, characterized in that: The reflectivity of the dielectric film (11) to the generated laser light is greater than 60%.

3. The ultrashort cavity high repetition rate fiber laser with adjustable repetition rate according to claim 1, characterized in that: The modulation depth of the semiconductor saturable absorption mirror (5) is 1% to 10%.

4. The ultrashort cavity high repetition rate fiber laser with adjustable repetition rate according to claim 1, characterized in that: The gain optical fiber is a rare earth ion doped optical fiber, and the doped rare earth ions include one or more of erbium, ytterbium, thulium and holmium.

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