Hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials

Abstract

The invention discloses a hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials, belonging to the field of passive mode-locked fiber lasers; the laser comprises a pump source, and a wavelength division multiplexer, an ytterbium-doped fiber, an SM-28e single-mode fiber, a polarization controller 1, a polarization-dependent isolator, a polarization controller 2, a coupler and a composite saturable absorber mode-locker are sequentially arranged in series in the light emission direction of the pump source; the polarization-dependent isolator is sandwiched between the polarization controller 1 and the polarization controller 2 to form a nonlinear polarization rotation structure, and realizes a double nonlinear absorption effect with the composite saturable absorber mode-locker; the film in the composite saturable absorber mode-locker is composited by single-walled carbon nanotubes and molybdenum disulfide solution, obtains more excellent optical properties on the basis of the initial properties of a single material, and can better lock the mode; and under the joint action of the nonlinear polarization rotation structure, the output performance of the ultrashort pulse laser is further improved.

Description

Technical Field

[0001] The invention belongs to the field of passive mode-locked fiber lasers, and in particular relates to a hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials. Background Art

[0002] Ytterbium-doped fiber laser is a laser that generates laser beams in optical fibers doped with ytterbium ions. It is widely used in manufacturing processes, medical treatments and other fields due to its advantages such as narrow pulse width, high output power and long working life. Due to the high doping concentration of ytterbium ions in ytterbium-doped fiber, compared with the more commonly used erbium-doped fiber lasers used in the 1550nm band, ytterbium-doped fiber lasers only need shorter ytterbium-doped fibers to obtain higher optical gain.

[0003] Passively mode-locked fiber lasers are considered to be the most effective and potential soliton source devices, but they also have some disadvantages. Taking various mode-locked structures as an example, real saturable absorbers usually have relatively low damage thresholds and short lifetimes, which also hinder the operation of lasers at high energy levels; the nonlinear polarization rotation effect is sensitive to the environment and is difficult to achieve self-starting.

[0004] In recent years, most ytterbium-doped fiber lasers use a single nonlinear polarization rotation structure or a single saturable absorber for mode-locked pulse output. Therefore, combining the two to use hybrid mode locking can effectively combine the advantages of the first two methods and avoid the disadvantages of the first two methods. Summary of the invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials, which solves the problems in the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials, comprising a pump source for outputting pump light, wherein a wavelength division multiplexer, an ytterbium-doped optical fiber, an SM-28e single-mode optical fiber, a polarization controller 1, a polarization-dependent isolator, a polarization controller 2, a coupler, and a composite saturable absorber mode-locker are sequentially arranged in series in the light emission direction of the pump source;

[0008] The polarization-dependent isolator is sandwiched between the first polarization controller and the second polarization controller to form a nonlinear polarization rotation structure, and realizes a dual nonlinear absorption effect with the composite saturable absorber mode locker.

[0009] Furthermore, the composite saturable absorber mode locker comprises two jumper heads and a film located between the two jumper heads, wherein the film is made of a single-walled carbon nanotube and a molybdenum disulfide solution by a liquid phase exfoliation method.

[0010] Furthermore, the film is cut into slices and clamped between two jumper heads and fixed with a flange.

[0011] Furthermore, the diameter of the single-walled carbon nanotube is 0.78 nm.

[0012] Furthermore, the core diameter of the ytterbium-doped optical fiber is 6 um and the length is 1 m; the total length of the SM-28e single-mode optical fiber is 17 m; the pigtails of the polarization controller 1 and the polarization controller 2 are both HI1060 single-mode optical fibers, and the lengths are both 1 m.

[0013] Furthermore, the total length of the laser cavity is 26m.

[0014] Furthermore, the dual wavelengths of the wavelength division multiplexer are 980nm and 1550nm, respectively, the loss is 0.13dB, and the isolation is 20.68db and 21.78dB, respectively.

[0015] Furthermore, the ytterbium-doped optical fiber gain coefficient is 250 dB / m.

[0016] Furthermore, the output ratio of the coupler is 10%:90%, and 10% of the light outputted from the output end of the coupler is used to detect the spectrum, and its pigtail is a HI1060 single-mode optical fiber;

[0017] The polarization-dependent isolator has an operating wavelength of 1030 nm, and its pigtail is a HI1060 single-mode optical fiber.

[0018] A laser cutting device comprises the above-mentioned hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention arranges single-walled carbon nanotubes and molybdenum disulfide in a composite saturable absorber mode locker, thereby obtaining more excellent optical properties based on the initial properties of a single material, and enabling better mode locking operation; in addition, the nonlinear polarization rotation structure works together to further improve the output performance of ultrashort pulse lasers.

[0021] 2. The hybrid mode-locking that combines the two mode-locking methods, the nonlinear polarization rotation structure and the saturable absorber mode-locking technology, is not only more stable in performance and has a high damage threshold, but can also perform better mode-locking operations near the 1030nm band at high pulse energy.

[0022] 3. The laser of the present invention uses ytterbium-doped fiber as the laser gain medium, and the total cavity length is 26m. It belongs to a long cavity structure, which is easier to reach the mode-locked state and can carry higher pulse energy and reduce the pulse repetition frequency. For the long cavity structure, the net dispersion in the cavity is large, and the numerical simulation results show that the pulse width of the laser output pulse will increase with the increase of the cavity length. This large chirp pulse can carry higher pulse energy and reduce the pulse repetition frequency, which is exactly the purpose of the traditional chirp amplification system to perform multi-stage processing on the pulse. Therefore, the pulse fiber laser with a long cavity structure can realize a simplified chirp amplification system, and then achieve high-energy pulse output.

[0023] 4. The laser of the present invention has the advantages of simple and compact structure and low cost; the low-loss fusion between optical fibers improves the coupling efficiency, and the light is always confined in the optical fiber in the laser cavity, which also largely avoids interference from external factors and improves environmental stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 It is a schematic diagram of the overall structure of the hybrid mode-locked picosecond laser of the present invention;

[0026] Figure 2 is a spectrum diagram of the picosecond laser in the present invention;

[0027] Figure 3 is an oscilloscope diagram of the picosecond laser in the present invention;

[0028] Figure 4 is a long-range spectrum diagram of the picosecond laser in the present invention;

[0029] Figure 5 is the output pulse spectrum diagram of the picosecond laser in the present invention;

[0030] Figure 6 It is a single pulse sequence diagram of the picosecond laser in the present invention.

[0031] In the figure: 1-pump source, 2-wavelength division multiplexer, 3-ytterbium-doped fiber, 4-SM-28e single-mode fiber, 5-polarization controller 1, 6-polarization dependent isolator, 7-polarization controller 2, 8-coupler, 9-composite saturable absorber mode locker. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] like Figure 1 As shown, a hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials includes a pump source 1 for outputting pump light, and a wavelength division multiplexer 2, an ytterbium-doped optical fiber 3, an SM-28e single-mode optical fiber 4, a polarization controller 1 5, a polarization-dependent isolator 6, a polarization controller 2 7, a coupler 8, and a composite saturable absorber mode locker 9 are sequentially arranged in the light output direction of the pump source 1;

[0035] The central wavelength of the pump light output by the pump source 1 is 974 nm.

[0036] The dual wavelengths of the wavelength division multiplexer 2 are 980nm and 1550nm, respectively, with a loss of 0.13dB and isolations of 20.68db and 21.78dB respectively.

[0037] The core diameter of the ytterbium-doped optical fiber 3 is 6 um and the length is 1 m; the gain coefficient of the ytterbium-doped optical fiber 3 is 250 dB / m.

[0038] The total length of the SM-28e single-mode optical fiber 4 is 17m. SM-28e is a commonly used single-mode optical fiber model that complies with the ITU-TG.652.D standard.

[0039] The pigtails of polarization controller 1 5 and polarization controller 2 7 are both HI1060 single-mode optical fibers, and both have a length of 1 m.

[0040] The polarization-dependent isolator 6 has an operating wavelength of 1030 nm, includes an input end and an output end, and the pigtail is a HI1060 single-mode optical fiber.

[0041] The output ratio of the coupler 8 is 10%:90%, and 10% of the light output from the output end of the coupler is used to detect the spectrum, and its pigtail is a HI1060 single-mode optical fiber.

[0042] In this embodiment, the composite saturable absorber mode locker 9 includes two jumper heads and a film located between the two jumper heads, wherein the film is made of a single-walled carbon nanotube with a tube diameter of 0.78 nm and a molybdenum disulfide solution by liquid phase exfoliation; after the film is made, it is cut into 2 mm 2 A square sheet of the same size is then clamped between the two jumper heads and fixed with a flange.

[0043] The pump light enters the ring cavity through the input end of the wavelength division multiplexer 2 via a single-mode jumper coupling, and the light with a wavelength of 974nm passes through the ytterbium-doped optical fiber 3 with a length of 1m and a gain coefficient of 250dB / m. The ytterbium-doped optical fiber 3 serves as a working medium for realizing stimulated emission light amplification to excite the doped ions and transform them into light with a wavelength of 1030nm. The signal light output from the ytterbium-doped optical fiber 3 enters the polarization controller 1 5 via the SM-28e single-mode optical fiber 4. The polarization state of the output light can be changed by adjusting the polarization controller 1 5 and the polarization controller 2 7. The polarization-dependent isolator 6 is sandwiched between the polarization controller 1 5 and the polarization controller 2 7 to form a nonlinear polarization rotation structure, and realizes a dual nonlinear absorption effect with the composite saturable absorber mode locker 9. The output end of the polarization controller 2 7 is connected to the coupler 8. The output of the entire ring laser cavity is connected to a single-mode jumper for output through the output end of the coupler 8 with a splitting ratio of 10%. After the output, the remaining 90% of the light continues to be looped into the cavity. At this time, the energy in the cavity is relatively low. The composite saturable absorber mode locker 9 is subsequently connected to prevent it from being broken down by excessive energy. The model of the pigtail of the above device is HI1060 single-mode optical fiber. The nonlinear polarization rotation structure of this embodiment and the composite saturable absorber mode locker 9 work together to form a hybrid mode locking mechanism.

[0044] The invented laser uses ytterbium-doped fiber as the laser gain medium, with a total cavity length of 26m. It has a long cavity structure, which makes it easier to reach a mode-locked state and can carry higher pulse energy and reduce the pulse repetition frequency.

[0045] Example 2

[0046] In this embodiment, the performance of the laser of the present invention (the laser in Embodiment 1) is tested;

[0047] like Figure 2 As shown, as the pump intensity increases to about 215mW, a typical approximately rectangular dissipative soliton spectrum is observed. The 3dB spectral bandwidth of the laser at the central wavelength of 1036.4nm is measured to be 15.5nm. The spectrum is characterized by a relatively flat middle part and steep edges, and is rectangular as a whole. It is a typical approximately rectangular dissipative soliton spectrum with good surface beam quality and relatively good stability.

[0048] like Figure 3 As shown, the optical signal is converted into an electrical signal by a photodetector (Thorlabs, 5 GHz), and the basic repetition frequency of the laser output pulse train is measured by an oscilloscope (R&S, RTP, 16 GHz). It is 7.198 MHz and the pulse period is 138.9 ns, corresponding to a laser cavity length of 26 m.

[0049] like Figure 4Figure 2 shows the pulse spectrum over 500 MHz. The signal-to-noise ratio is high and stable over a long period of time, which indicates that the intensity fluctuations of the pulses are small and indicates stable mode-locked operation of the fiber laser.

[0050] like Figure 5 As shown, the spectrum of a single laser pulse measured using a spectrum analyzer is shown, with a signal-to-noise ratio of 55 dB, indicating that the laser can still achieve stable single-wavelength mode locking in the 1036.4 nm band.

[0051] like Figure 6 The figure shows a single pulse sequence of the laser pulse output, with a pulse width of 416.8ps. Since the long cavity brings stronger nonlinear accumulation, it also brings higher dispersion in the cavity, so the pulse width of the output pulse is wider.

[0052] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0053] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. Hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials, characterized in that: The invention comprises a pump source (1) for outputting pump light, wherein the light output direction of the pump source (1) is sequentially connected to a wavelength division multiplexer (2), an ytterbium-doped optical fiber (3), an SM-28e single-mode optical fiber (4), a polarization controller 1 (5), a polarization-dependent isolator (6), a polarization controller 2 (7), a coupler (8), and a composite saturable absorber mode locker (9); a first input end and a second input end of the wavelength division multiplexer (2) are respectively connected to the pump source (1) and the composite saturable absorber mode locker (9), and an output end of the wavelength division multiplexer (2) is connected to the ytterbium-doped optical fiber (3); The polarization-dependent isolator (6) is sandwiched between the first polarization controller (5) and the second polarization controller (7) to form a nonlinear polarization rotation structure, and realizes a dual nonlinear absorption effect with the composite saturable absorber mode locker (9); The composite saturable absorber mode locker (9) comprises two jumper heads and a film located between the two jumper heads, wherein the film is made by combining single-walled carbon nanotubes and molybdenum disulfide solution through a liquid phase exfoliation method.

2. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: After the film is cut into slices, it is clamped between two jumper heads and fixed with a flange.

3. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: The diameter of the single-walled carbon nanotube is 0.78 nm.

4. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: The core diameter of the ytterbium-doped optical fiber (3) is 6 μm and the length is 1 m; the total length of the SM-28e single-mode optical fiber (4) is 17 m; the pigtails of the polarization controller 1 (5) and the polarization controller 2 (7) are both HI1060 single-mode optical fibers and are both 1 m in length.

5. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1 or 4, characterized in that: The total length of the laser cavity is 26m.

6. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: The dual wavelengths of the wavelength division multiplexer (2) are 980 nm and 1550 nm respectively, the loss is 0.13 dB, and the isolation is 20.68 dB and 21.78 dB respectively.

7. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: The ytterbium-doped optical fiber (3) has a gain coefficient of 250 dB / m.

8. The hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials according to claim 1, characterized in that: The output ratio of the coupler (8) is 10%:90%, and 10% of the light outputted from the output end of the coupler (8) is used to detect the spectrum, and its pigtail is a HI1060 single-mode optical fiber; The polarization-dependent isolator (6) has an operating wavelength of 1030 nm, and its pigtail is a HI1060 single-mode optical fiber.

9. A laser cutting device, characterized in that: A hybrid mode-locked picosecond laser based on nonlinear polarization rotation and composite materials as described in any one of claims 1 to 8.

Images