Preparation Method of a Spatiotemporal Mode-Locked Fiber Laser Based on a Saturable Absorber

Abstract

The present invention relates to the technical field of fiber lasers, specifically to a preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. In the preparation process, an InP quantum dot saturable absorber is used as the absorber, and the specific steps are as follows: preparation of InP quantum dots; preparation of an InP quantum dot saturable absorber. The present invention uses a saturable absorber of InP quantum dots with a large modulation depth and a low saturation intensity to prepare a spatio-temporal mode-locked fiber laser, which can synchronously lock multiple transverse and longitudinal modes to generate picosecond mode-locked pulses. By selecting a multimode gain fiber, it has a larger mode area, which can reduce the nonlinear effect to meet the growing demand for high-power lasers. Its additional spatial degree of freedom can improve the transmission capacity in optical communication.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber lasers, and specifically to a preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. Background Technique

[0002] Ultrafast pulsed lasers have important research and application values in the fields of precision machining, biomedical treatment, scientific research, etc. Especially for ultrashort pulsed fiber lasers, which have the advantages of simple structure, stable light output performance, maintenance-free, easy to carry, etc., and have become preferred high-tech tools in all walks of life. However, currently, the relatively mature ultrafast fiber lasers are all built based on single-mode fibers. At medium peak powers, due to the small core of single-mode fibers, strong nonlinear effects will occur, and the accumulation of nonlinear phases will break the pulses, restricting the further improvement of energy. In addition, in the current era of data explosion, the transmission of a large amount of data is also a huge challenge for single-mode fibers. Therefore, due to the limitation of the mode area, single-mode fibers are restricted in improving power and space-division multiplexing. Using multi-mode fibers with a large core diameter is an effective way to overcome the above limitations. Multi-mode fibers have a larger modal area, which can reduce nonlinear effects to meet the growing high-power laser requirements, and their additional spatial degrees of freedom can increase the transmission capacity in optical communication. Multi-mode fiber mode-locked fiber lasers can synchronously lock multiple transverse and longitudinal modes, that is, spatio-temporal mode locking.

[0003] Passive mode locking is a method that can be used to generate ultrashort pulsed lasers. Its basic principle is to add a saturable absorber in the optical path. After the light source passes through the saturable absorber, the loss of the side wings is greater than that of the central part, resulting in the narrowing of the optical pulse, thereby generating an ultrashort pulsed laser. Thus, it can be seen that the saturable absorber is the most important component of the ultrashort pulsed laser. Therefore, developing a new type of saturable absorber material to realize an all-fiber spatio-temporal mode-locked ultrafast laser has become a meaningful work. In view of this, we propose a preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. Summary of the Invention

[0004] To make up for the above deficiencies, the present invention provides a preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber.

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber, wherein the absorber in the preparation process adopts an InP quantum dot saturable absorber, and specifically includes the following steps:

[0007] Preparation of InP quantum dots:

[0008] S1. Mix the raw materials to obtain a primary mixture, and perform a vacuum pumping treatment on the primary mixture;

[0009] S2. Heat-treat the primary mixture obtained in S1;

[0010] S3. Inject a zinc precursor solution into the heat-treated mixture and mix to obtain a secondary mixture;

[0011] S4. Heat-treat the secondary mixture obtained in S3 by raising the temperature again;

[0012] S5. Inject dodecanethiol into the mixture after the secondary heat treatment and mix to obtain a tertiary mixture, and then raise the temperature for heat treatment again;

[0013] S6. Naturally cool to room temperature after the reaction ends;

[0014] S7. Centrifuge the product obtained in S6 at high speed, then take out the supernatant, add ethanol to the supernatant until the solution becomes turbid, centrifuge again and dissolve the precipitate in n-hexane, add ethanol again and then perform centrifugation, and finally disperse the obtained precipitate;

[0015] Preparation of InP quantum dot saturable absorber:

[0016] Drop the prepared InP quantum dot solution onto the tapered optical fiber and let it air-dry naturally to obtain the saturable absorber;

[0017] Preparation of fiber laser:

[0018] Use an optical fiber fusion splicer to sequentially connect a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, a coupler, a polarization controller, and a saturable absorber in a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain a fiber laser.

[0019] As a preferred technical solution of the present invention, the raw materials in S1 are InI3, ZnBr2 and oleylamine, the In / Zn molar ratio = 1:6.5, the mixing container uses a three-necked flask, the temperature for vacuum pumping of the primary mixture is 110°C - 130°C, and the vacuum pumping time is 15 min - 25 min.

[0020] As a preferred technical solution of the present invention, in S2, the primary mixture is heated to 190°C - 210°C, and 0.45 mL of tris(dimethylamino)phosphine is quickly injected during the heating process.

[0021] As a preferred technical solution of the present invention, the composition of the zinc precursor solution in S3 is zinc stearate with a content of 3 g, which is dissolved in 12 ml of octadecene, and 1.5 ml of (2.2 M) Top(Se + S) solution is injected into the secondary mixture.

[0022] As a preferred technical solution of the present invention, the temperature in S4 is increased to 250°C - 270°C and maintained for 100 min - 140 min.

[0023] As a preferred technical solution of the present invention, the content of 1-dodecanethiol injected in S5 is 1.5 ml, and the temperature is increased to 270°C - 290°C and maintained for 50 min - 70 min.

[0024] As a preferred technical solution of the present invention, the rotation speed of the centrifugation treatment in S7 is 11000 rpm, and the obtained precipitate is dispersed in 10 ml of n-hexane solution.

[0025] As a preferred technical solution of the present invention, the diameter of the tapered fiber in step two is 9 μm.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The present invention uses a saturable absorber of InP quantum dots with a large modulation depth and a low saturation intensity to prepare a spatio-temporal mode-locked fiber laser, which can synchronously lock multiple transverse and longitudinal modes to generate picosecond mode-locked pulses. By selecting a multimode gain fiber, it has a larger mode area, which can reduce the nonlinear effect to meet the growing high-power laser demand, and its additional spatial degree of freedom can increase the transmission capacity in optical communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of a ring-cavity spatio-temporal mode-locked fiber laser based on a saturable absorber in the present invention;

[0029] Figure 2 is an absorption spectrum diagram of an InP quantum dot solution in the present invention;

[0030] Figure 3 is a transmission electron microscope image of InP quantum dots in the present invention;

[0031] Figure 4 is a pulse sequence diagram of an experimental measurement of a ring-cavity spatio-temporal mode-locked fiber laser based on a saturable absorber in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0034] Example 1. The above technical solution will be described in detail through the following examples:

[0035] A preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. In the preparation process, the absorber uses an InP quantum dot saturable absorber, which specifically includes the following steps:

[0036] Preparation of InP quantum dots:

[0037] S1. Mix the raw materials to obtain a primary mixture, and evacuate the primary mixture.

[0038] S2. Heat the primary mixture obtained through S1.

[0039] S3. Inject a zinc precursor solution into the mixture after heat treatment and mix to obtain a secondary mixture.

[0040] S4. Heat the mixed secondary mixture obtained through S3 again for temperature increase treatment.

[0041] S5. Inject 1-dodecanethiol into the mixture after secondary heat treatment and mix to obtain a tertiary mixture, and then heat it again for temperature increase treatment.

[0042] S6. Naturally cool to room temperature after the reaction ends.

[0043] S7. Centrifuge the product obtained through S6 at high speed, then take out the supernatant. Add ethanol to the supernatant until the solution becomes turbid, centrifuge again, take the precipitate and dissolve it in n-hexane. Add ethanol again and then perform centrifugation treatment. Finally, disperse the obtained precipitate.

[0044] Preparation of InP quantum dot saturable absorber:

[0045] Drop the prepared InP quantum dot solution on the tapered fiber and let it dry naturally to obtain the saturable absorber.

[0046] Preparation of fiber laser:

[0047] Use an optical fiber fusion splicer to sequentially connect a wavelength division multiplexer, gain fiber, polarization-independent isolator, coupler, polarization controller, and saturable absorber in a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain a fiber laser.

[0048] As an optimization of this embodiment, in S1, the raw materials are InI3, ZnBr2, and oleylamine, the molar ratio of In / Zn = 1:6.5, the mixing container is a three-necked flask, the temperature for evacuating the primary mixture is 120 °C, and the evacuation time is 20 min.

[0049] As an optimization of this embodiment, in S2, heat the primary mixture to 200 °C and quickly inject 0.45 mL of tris(dimethylamino)phosphine during the heating process.

[0050] As an optimization of this embodiment, the composition of the zinc precursor solution in S3 is zinc stearate with a content of 3 g, dissolve it in 12 ml of octadecene, and inject 1.5 ml of (2.2 M) Top(Se+S) solution into the secondary mixture.

[0051] As an optimization of this embodiment, raise the temperature in S4 to 260 °C and maintain it for 120 minutes.

[0052] As an optimization of this embodiment, the content of 1-dodecanethiol injected in S5 is 1.5 ml, and raise the temperature to 280 °C and maintain it for 60 min.

[0053] As an optimization of this embodiment, the rotation speed for centrifugation in S7 is 11000 rpm, and disperse the obtained precipitate in 10 ml of n-hexane solution.

[0054] As an optimization of this embodiment, the diameter of the tapered fiber in step 2 is 9 μm.

[0055] It should be added that, as Figure 1 shown, the fiber pulse laser in this embodiment adopts a ring cavity structure, the gain fiber is a ytterbium-doped fiber, the wavelength of the pump source is 980 nm, and the central wavelength of the wavelength division multiplexer is 1064 nm. Use an optical fiber fusion splicer to sequentially connect the wavelength division multiplexer, gain fiber, polarization-independent isolator, coupler, polarization controller, and saturable absorber in Figure 1 a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain a fiber laser.

[0056] By adding a saturable absorber in the optical path, after the light passes through the saturable absorber, the loss of the side wing part is greater than that of the central part, resulting in the narrowing of the optical pulse, thereby generating ultrashort pulse laser.

[0057] By selecting a multimode gain fiber, increasing the mode area, reducing the nonlinear effect, and synchronously locking multiple transverse and longitudinal modes, the growing demand for high-power lasers can be met. In addition, its additional spatial degrees of freedom can also increase the transmission capacity in optical communication.

[0058] Embodiment 2. The above technical solution will be described in detail through the following embodiments:

[0059] A preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. In the preparation process, an InP quantum dot saturable absorber is used for the absorber, which specifically includes the following steps:

[0060] Preparation of InP quantum dots:

[0061] S1. Mix the raw materials to obtain a primary mixture, and perform a vacuum treatment on the primary mixture;

[0062] S2. Heat the primary mixture obtained through S1;

[0063] S3. Inject a zinc precursor solution into the mixture after the heat treatment and mix to obtain a secondary mixture;

[0064] S4. Heat the secondary mixed mixture obtained through S3 again;

[0065] S5. Inject dodecanethiol into the mixture after the secondary heat treatment and mix to obtain a tertiary mixture, and heat it again;

[0066] S6. Naturally cool to room temperature after the reaction ends;

[0067] S7. Centrifuge the product obtained through S6 at high speed, then take out the supernatant, add ethanol to the supernatant until the solution becomes turbid, centrifuge again to take the precipitate, wash twice repeatedly in this way, and finally disperse the obtained precipitate;

[0068] Preparation of InP quantum dot saturable absorber:

[0069] Drop the prepared InP quantum dot solution on the tapered fiber and air-dry it to obtain the saturable absorber;

[0070] Preparation of the fiber laser:

[0071] Use an optical fiber fusion splicer to sequentially connect a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, a coupler, a polarization controller, and a saturable absorber in a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain the fiber laser.

[0072] Preferably in this embodiment, the raw materials in S1 are InI3, ZnBr2 and oleylamine, the In / Zn molar ratio = 1:6.5, the mixing container is a three-necked flask, the temperature for vacuum pumping of the primary mixture is 110 °C, and the vacuum pumping time is 15 min.

[0073] Preferably in this embodiment, in S2, the primary mixture is heated to 190 °C, and 0.45 mL of tris(dimethylamino)phosphine is rapidly injected during the heating process.

[0074] Preferably in this embodiment, the composition of the zinc precursor solution in S3 is zinc stearate with a content of 3 g, which is dissolved in 12 ml of octadecene, and 1.5 ml of (2.2 M) Top(Se + S) solution is injected into the secondary mixture.

[0075] Preferably in this embodiment, the temperature in S4 is raised to 250 °C and maintained for 100 min.

[0076] Preferably in this embodiment, the content of 1-dodecanethiol injected in S5 is 1.5 ml, and the temperature is raised to 270 °C and maintained for 50 min.

[0077] Preferably in this embodiment, the rotation speed of the centrifugation treatment in S7 is 11,000 rpm, and the obtained precipitate is dispersed in 10 ml of n-hexane solution.

[0078] Preferably in this embodiment, the diameter of the tapered optical fiber in step two is 9 μm.

[0079] It should be added that as Figure 1 shown, the fiber pulse laser in this embodiment adopts a ring cavity structure, the gain fiber is a ytterbium-doped fiber, the wavelength of the pump source is 980 nm, and the central wavelength of the wavelength division multiplexer is 1064 nm. The wavelength division multiplexer, gain fiber, polarization-independent isolator, coupler, polarization controller, and saturable absorber are sequentially connected in the order of Figure 1 to form a ring resonator; and the other end of the wavelength division multiplexer is connected to the pump light source to obtain a fiber laser.

[0080] By adding a saturable absorber in the optical path, after the light passes through the saturable absorber, the loss of the wing part is greater than that of the central part, resulting in the narrowing of the optical pulse, thereby generating ultrashort pulse laser.

[0081] By selecting a multimode gain fiber, increasing the modal area, reducing the nonlinear effect, and synchronously locking multiple transverse and longitudinal modes, the growing high-power laser requirements can be met. In addition, its additional spatial degree of freedom can also increase the transmission capacity in optical communication.

[0082] Example 3. The above technical solution is described in detail through the following examples:

[0083] A preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber. In the preparation process, the absorber uses an InP quantum dot saturable absorber, which specifically includes the following steps:

[0084] Preparation of InP quantum dots:

[0085] S1. Mix the raw materials to obtain a primary mixture, and perform a vacuum treatment on the primary mixture;

[0086] S2. Heat the primary mixture obtained through S1;

[0087] S3. Inject a zinc precursor solution into the heated mixture and mix to obtain a secondary mixture;

[0088] S4. Heat the mixed secondary mixture obtained through S3 again;

[0089] S5. Inject dodecanethiol into the mixture obtained through the secondary heating treatment and mix to obtain a tertiary mixture, and heat it again;

[0090] S6. Naturally cool to room temperature after the reaction ends;

[0091] S7. Perform high-speed centrifugation on the product obtained through S6, then take out the supernatant, add ethanol to the supernatant until the solution becomes turbid, centrifuge again to obtain the precipitate, wash twice in this way, and finally disperse the obtained precipitate;

[0092] Preparation of InP quantum dot saturable absorber:

[0093] Drop the prepared InP quantum dot solution on the tapered fiber and let it dry naturally to obtain the saturable absorber;

[0094] Preparation of fiber laser:

[0095] Use an optical fiber fusion splicer to connect a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, a coupler, a polarization controller, and a saturable absorber in a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain a fiber laser.

[0096] As a preference of this example, the raw materials in S1 are InI3, ZnBr2, and oleylamine, the In / Zn molar ratio = 1:6.5, the mixing container uses a three-necked flask, the temperature for vacuum treatment of the primary mixture is 130 °C, and the vacuum treatment time is 25 min.

[0097] Preferably in this embodiment, in S2, the primary mixture is heated to 210 °C, and 0.45 mL of tris(dimethylamino)phosphine is rapidly injected during the heating process.

[0098] Preferably in this embodiment, the composition of the zinc precursor solution in S3 is zinc stearate with a content of 3 g, which is dissolved in 12 ml of octadecene, and 1.5 ml of (2.2 M) Top(Se + S) solution is injected into the secondary mixture.

[0099] Preferably in this embodiment, in S4, the temperature is raised to 270 °C and maintained for 130 min.

[0100] Preferably in this embodiment, in S5, the content of 1-dodecanethiol injected is 1.5 ml, and the temperature is raised to 290 °C and maintained for 70 min.

[0101] Preferably in this embodiment, in S7, the rotation speed of the centrifugation treatment is 11,000 rpm, and the obtained precipitate is dispersed in 10 ml of n-hexane solution.

[0102] Preferably in this embodiment, the diameter of the tapered optical fiber in step two is 9 μm.

[0103] It should be added that, as Figure 1 shown, the fiber pulse laser in this embodiment adopts a ring cavity structure. The gain fiber is a ytterbium-doped fiber. The wavelength of the pump source is 980 nm, and the central wavelength of the wavelength division multiplexer is 1064 nm. The wavelength division multiplexer, the gain fiber, the polarization-independent isolator, the coupler, the polarization controller, and the saturable absorber are sequentially connected in accordance with Figure 1 the order to form a ring resonator; and the other end of the wavelength division multiplexer is connected to the pump light source to obtain a fiber laser.

[0104] By adding a saturable absorber in the optical path, after the light passes through the saturable absorber, the loss of the side wing part is greater than that of the central part, resulting in the narrowing of the optical pulse, thereby generating an ultrashort pulse laser.

[0105] By selecting a multimode gain fiber, increasing the mode area, reducing the nonlinear effect, and synchronously locking multiple transverse and longitudinal modes, the growing high-power laser requirements can be met. In addition, its additional spatial degrees of freedom can also increase the transmission capacity in optical communication.

[0106] As Figure 2As shown, it is the absorption spectrum of the InP quantum dot solution in Examples 1-3. It can be seen from the figure that its absorption peak is approximately at 483 nm. The absorption peak of the material characterizes its bandgap as a saturable absorber because the size of the bandgap has an impact on its performance as a saturable absorber. It can be seen from this absorption peak value that the bandgap of the saturable absorber is small, which has little impact on the saturable absorber itself.

[0107] As Figure 3 shown, it is the transmission electron microscope image of the InP quantum dots in Examples 11-3. The size distribution of the InP quantum dots is uniform, and the size is about 4-6 nm.

[0108] As Figure 4 shown is the pulse sequence diagram of the ring-cavity spatio-temporal mode-locked fiber laser based on the InP quantum dot saturable absorber measured experimentally, which shows that the laser has a stable mode-locked pulse output. It can be clearly seen from this pulse sequence diagram that the laser in this embodiment can generate mode-locked pulses, converting the continuous light of the light source into pulsed light after passing through this constructed optical path. In this process, the InP quantum dot saturable absorber is the key device to achieve this function.

[0109] 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 by the above embodiments. The above embodiments and descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. Preparation method of a spatio-temporal mode-locked fiber laser based on a saturable absorber, characterized in that: In the preparation process, the absorber uses an InP quantum dot saturable absorber, and the specific steps are as follows: Preparation of InP quantum dots: S1. Mix the raw materials to obtain a primary mixture, and subject the primary mixture to vacuum treatment; S2. Heat the primary mixture obtained in S1; S3. Inject a zinc precursor solution into the mixture after heat treatment and mix to obtain a secondary mixture; S4. Heat the secondary mixture obtained in S3 again by raising the temperature; S5. Inject 1-dodecanethiol into the mixture after secondary heat treatment and mix to obtain a tertiary mixture, and heat it again by raising the temperature; S6. Naturally cool to room temperature after the reaction ends; S7. Centrifuge the product obtained in S6 at a high speed, then take out the supernatant, add ethanol to the supernatant until the solution becomes turbid, centrifuge again to obtain the precipitate, wash it twice in this way, and finally disperse the obtained precipitate; Preparation of InP quantum dot saturable absorber: Drop the prepared InP quantum dot solution on the tapered fiber, and let it air-dry naturally to obtain the saturable absorber; Preparation of fiber laser: Use a fiber fusion splicer to connect a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, a coupler, a polarization controller, and a saturable absorber in a specific order to form a ring resonator; and connect the other end of the wavelength division multiplexer to the pump light source to obtain a fiber laser; In S1, the raw materials are InI3, ZnBr2, and oleylamine, the In / Zn molar ratio = 1:6.5, the mixing container uses a three-neck flask, the vacuum temperature of the primary mixture is 110°C - 130°C, and the vacuum time is 15 min - 25 min; In the zinc precursor solution in S3, the composition is zinc stearate with a content of 3 g, which is dissolved in 12 ml of octadecene, and 1.5 ml of (2.2M) Top(Se+S) solution is injected into the secondary mixture.

2. The preparation method of the spatio-temporal mode-locked fiber laser based on a saturable absorber according to claim 1, characterized in that: In S2, heat the primary mixture to 190°C - 210°C, and quickly inject 0.45 mL of tris(dimethylamino)phosphine during the heating process.

3. The preparation method of the spatio-temporal mode-locked fiber laser based on a saturable absorber according to claim 1, characterized in that: In S4, raise the temperature to 250°C - 270°C and maintain it for 100 min - 140 min.

4. The preparation method of the spatio-temporal mode-locked fiber laser based on a saturable absorber according to claim 1, wherein: In S5, the content of 1-dodecanethiol injected is 1.5 ml, and raise the temperature to 270°C - 290°C and maintain it for 50 min - 70 min.

5. The preparation method of the spatio-temporal mode-locked fiber laser based on a saturable absorber according to claim 1, characterized in that: In S7, the rotation speed of the centrifugation treatment is 11000 rpm, and the obtained precipitate is dispersed in 10 ml of n-hexane solution.

6. The preparation method of the spatio-temporal mode-locked fiber laser based on a saturable absorber according to claim 1, characterized in that: The diameter of the tapered fiber is 9 μm.

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