All-fiber space-time mode-locked laser with controllable high-order transverse mode

Abstract

The utility model discloses a high-order transverse mode controllable space-time mode locking all-fiber laser, which relates to the field of fiber lasers and comprises an annular laser system and a feedback system. The ring laser system comprises a laser diode pumping source, a wavelength division multiplexer, a gain fiber, a high-order transverse mode generation module, a multi-mode output coupler, a saturable absorber, a polarization controller, an isolator and an out-of-cavity coupler. The feedback control system comprises an image acquisition module, an image processing module and a feedback control circuit. Space-time mode locking is achieved based on the all-fiber saturable absorber, and the device has the advantages of being simple in structure, small in environmental influence, good in stability and the like. By inserting the multi-core multimode optical fiber and the conical multimode optical fiber into the all-fiber mode-locked laser, excitation of a high-order transverse mode and screening of the high-order transverse mode are effectively achieved. By externally connecting a feedback control system, the high-order transverse mode output by the laser is selected, and the space-time mode-locked all-fiber laser with controllable output high-order transverse mode is effectively realized.

Description

Technical Field

[0001] The utility model relates to the field of optical fiber lasers, and in particular to an all-optical fiber time-space mode-locked laser with controllable high-order transverse modes. Background Art

[0002] Multimode optical fiber can support multiple transverse modes, so it has additional spatial freedom compared to single-mode optical fiber, and also breaks through the power transmission limit of single-mode optical fiber. Multimode optical fiber contains a variety of nonlinear effects, making it an extremely advantageous waveguide in the field of lasers. Among them, Kerr nonlinear self-purification effect, geometric parameter instability, supercontinuum generation, saturable absorption effect, and space-time mode locking are nonlinear effects closely related to ultrashort pulse lasers. In 2017, the first space-time mode lock based on multimode optical fiber was patented. By adjusting the dispersion in the laser resonant cavity, different transverse and longitudinal modes are locked simultaneously to form multimode ultrashort pulses.

[0003] At present, spatiotemporal mode locking has been achieved through nonlinear multimode interference mode locking, nonlinear polarization selective mode locking, SESAM mode locking combined with multimode fiber, but there is no way to control the order of high-order transverse modes in spatiotemporal mode locking pulses. Therefore, the existing spatiotemporal mode-locked lasers need to be further optimized in terms of laser structure and high-order transverse mode selection capability. Utility Model Content

[0004] Existing spatiotemporal mode-locked fiber lasers based on multimode fibers can output spatiotemporal mode-locked pulses with high-order transverse modes, but the modes of the high-order transverse modes are uncontrollable. In view of this, the utility model proposes a spatiotemporal mode-locked fiber laser with controllable high-order transverse modes, which uses multi-core multimode fibers to excite high-order modes, and uses tapered single-mode fibers and feedback control systems to screen and select modes, thereby achieving mode-controllable pulse output, which has broad application prospects.

[0005] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0006] A high-order transverse mode controllable spatiotemporal mode-locked all-fiber laser comprises a ring laser system and a feedback system, wherein the ring laser system comprises a laser diode pump source, a wavelength division multiplexer, a gain fiber, a high-order transverse mode generation module, a multimode output coupler, a saturable absorber, a polarization controller, an isolator and an extracavity coupler; the laser diode pump source is connected to the input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the input end of the gain fiber, the output end of the gain fiber is connected to the input end of the high-order transverse mode generation module, and the output end of the high-order transverse mode generation module is connected to the common end of the multimode output coupler; the 10% output end of the multimode output coupler is used for outputting spatiotemporal mode-locked pulses, and the 90% output end of the multimode output coupler is used for connecting the input of the saturable absorber end, the output end of the saturable absorber is connected to the input end of the polarization controller, the output end of the polarization controller is connected to the input end of the isolator, the input end of the isolator is connected to the input end of the wavelength division multiplexer, the 1% output end of the extracavity coupler is connected to the feedback system, and the 99% output end of the extracavity coupler is used for the final output; the feedback control system includes an image acquisition module, an image processing module, and a feedback control circuit, the image acquisition module acquires the high-order transverse mode output from the output end of the multi-mode output coupler in the above-mentioned ring laser system; the image processing module converts the acquired image into a digital signal and inputs it into the feedback control circuit; the feedback control circuit generates a feedback control signal according to the input digital signal by setting a threshold, that is, the required high-order transverse mode.

[0007] Furthermore, the output wavelength of the laser diode pump source is 976 nm.

[0008] Furthermore, the wavelength division multiplexer is a 976 / 1064 nm three-port device, with two input ports, one with a central wavelength of 976 nm and one with a central wavelength of 1064 nm, and a common port with a central wavelength of 1064 nm.

[0009] Furthermore, the gain fiber is a single-mode or multi-mode gain fiber, and the total absorption of the gain fiber to the pump light is 20 dB.

[0010] Furthermore, the high-order transverse mode generation module includes an n-core multimode optical fiber (n=1, 2, 3...) and a tapered single-mode optical fiber, the multimode optical fiber is used to excite the high-order mode, and the tapered single-mode optical fiber is used to screen out the high-order mode.

[0011] Furthermore, the pigtail of the multimode output coupler is a gradient-index multimode optical fiber, which achieves proportional output of different high-order modes.

[0012] Furthermore, the saturable absorber is composed of two sections of Hi060 single-mode optical fibers with a section of gradient-index multimode optical fiber sandwiched between them. The core diameter or length of the gradient-index multimode optical fiber can be changed by a taper machine, thereby changing the saturable absorption characteristics.

[0013] Furthermore, the polarization controller is an in-line polarization controller, which can change the polarization state in the cavity by adjusting the upper knob, that is, the rotation angle, so as to control the laser mode field in the optical fiber to obtain a variety of high-order transverse modes.

[0014] Furthermore, the isolator is a polarization-independent isolator to ensure that light runs unidirectionally in the laser.

[0015] As a preferred solution, the saturable absorber may also be replaced by other saturable absorbers with better performance, such as some natural saturable absorbers and other equivalent saturable absorbers.

[0016] Furthermore, the image acquisition module uses a CCD device to acquire high-order transverse mode images at the output end of the multi-mode output coupler.

[0017] Furthermore, the feedback control circuit uses FPGA or other feedback circuits to judge the digital signal output by the digital image processing module, and is connected to the polarization controller in the laser system to generate a feedback signal and adjust the rotation angle to achieve feedback regulation.

[0018] The beneficial effects of the technical solution provided by the utility model are:

[0019] (1) The utility model realizes spatiotemporal mode locking based on an all-fiber saturable absorber, and has the advantages of simple structure, little environmental influence, and good stability.

[0020] (2) The utility model effectively realizes the excitation of high-order transverse modes and the screening of high-order transverse modes by inserting a multi-core multimode optical fiber and a tapered multimode optical fiber into an all-fiber mode-locked laser.

[0021] (3) The utility model selects the high-order transverse modes of the laser output by connecting an external feedback control system to the output end of the multi-mode output coupler in the spatiotemporal mode-locked all-fiber laser cavity, thereby effectively realizing a spatiotemporal mode-locked all-fiber laser with controllable output high-order transverse modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation of the utility model or the technical solution in the prior art, the following is a brief introduction to the drawings required for the specific implementation or the prior art description:

[0023] Figure 1 This is the overall structural diagram of the time-space mode-locked all-fiber laser with controllable high-order transverse modes.

[0024] Figure 2 This is the laser structure diagram of the time-space mode-locked all-fiber laser with controllable high-order transverse modes.

[0025] Figure 3 Diagram of the output feedback control system of a space-time mode-locked all-fiber laser with controllable high-order transverse modes.

[0026] Figure 4 This is the logic block diagram of the output feedback control system of the spatiotemporal mode-locked all-fiber laser.

[0027] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0028] 1: Laser diode pump source; 2: Wavelength division multiplexer; 3: Single-mode gain fiber; 4: High-order transverse mode generation module; 5: Multimode output coupler; 6: Saturable absorber; 7: Polarization controller; 8: Isolator; 9: Extracavity coupler; 10: Image acquisition module; 11: Image processing module 12: Feedback control circuit. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0030] Figure 1The overall structure of the time-space locked all-fiber laser with controllable high-order transverse mode is shown in Figure 1. The ring laser system includes: laser diode pump source 1, wavelength division multiplexer 2, gain fiber 3, high-order transverse mode generation module 4, multimode output coupler 5, saturable absorber 6, polarization controller 7, isolator 8, and extracavity coupler 9. The laser diode pump 1 with a central wavelength of 976 nm and the 976 nm of the wavelength division multiplexer 2 are connected. The right end of the wavelength division multiplexer 2 is connected to the left end of the gain fiber 3, and the gain fiber is pumped to produce a population inversion to obtain a laser; the right end of the gain fiber 3 is connected to the left end of the high-order transverse mode generation module 4, and the transmission light excites a high-order mode in the multi-core fiber, and the high-order mode is screened out through the tapered fiber; the right end of the high-order transverse mode generation module 4 is connected to the common end of the multi-mode output coupler 5, and the 10% output end of the multi-mode output coupler 5 is used for the output of the space-time mode-locked pulse, and the 90% output end of the multi-mode output coupler 5 is used to connect to the left end of the saturable absorber 6 and couple back to The cavity continues to oscillate; the right end of the saturable absorber 6 is connected to the left end of the polarization controller 7, and the graded refractive index multimode fiber and the single-mode fiber in the cavity form a single-mode-multimode-single-mode structure. When the optical signal passes through this structure, due to the existence of nonlinear effects such as self-phase modulation and cross-phase modulation in the multimode fiber, the high-power signal can obtain higher transmission efficiency than the low-power signal, so it can play the role of a saturable absorber required for mode locking; the right end of the polarization controller 7 is connected to the left end of the isolator to ensure the unidirectional operation of the laser in the cavity; the right end of the isolator 8 is connected to the left 1064 nm input end of the wavelength division multiplexer 2 to form a ring cavity fiber laser. In addition, the 1% output end of the extracavity coupler 9 is connected to the feedback control system, and the 99% output end is used for the final output. Elements 1-9 constitute Figure 2 The laser system shown in FIG. 1 includes a laser diode pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a high-order transverse mode generation module 4, a multimode output coupler 5, a saturable absorber 6, a polarization controller 7, and an isolator 8, which are manually spliced ​​using a fiber splicer.

[0031] Figure 3 This is the schematic diagram of the output feedback control system of the spatiotemporal mode-locked all-fiber laser. Figure 4 The output feedback system logic block diagram. The feedback system includes an image acquisition module 10, an image processing module 11, and a feedback control circuit 12. The image acquisition module 10 uses a CCD device to collect the high-order transverse mode output from the 1% output end of the multimode output coupler 9 in the above-mentioned ring laser system; the image processing module 11 converts the collected image information into a digital signal and inputs it into the feedback control circuit 12; the feedback control circuit 12 generates a feedback control signal according to the input digital signal by setting a threshold, that is, the required high-order transverse mode. If the output pulse is not the required high-order transverse mode (not equal to the set threshold), the feedback signal controls Figure 2The knob rotation angle of the in-line polarization controller 7 in the ring laser system shown To obtain a new high-order transverse mode, until the required high-order transverse mode pulse is obtained, the rotation angle controlled by the feedback signal becomes At this time, the output pulse is the required high-order transverse mode, thereby realizing a time-space mode-locked all-fiber laser with controllable output of high-order transverse modes.

[0032] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the utility model and are not used to limit the utility model. Without departing from the spirit and scope of the utility model, the utility model may have various changes and improvements, which fall within the scope of the utility model to be protected. The scope of protection of the utility model is defined by the attached claims and their equivalents.

Claims

1. An all-fiber spatiotemporal mode-locked laser with controllable high-order transverse modes, characterized in that: The invention comprises a ring laser system and a feedback control system, wherein the ring laser system comprises a laser diode pump source, a wavelength division multiplexer, a gain fiber, a high-order transverse mode generation module, a multimode output coupler, a saturable absorber, a polarization controller, an isolator and an extracavity coupler; the laser diode pump source is connected to the input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to the input end of the gain fiber, the output end of the gain fiber is connected to the input end of the high-order transverse mode generation module, and the output end of the high-order transverse mode generation module is connected to the common end of the multimode output coupler; the 10% output end of the multimode output coupler is used for outputting a spatiotemporal mode-locked pulse, the 90% output end of the multimode output coupler is used for connecting the input end of the saturable absorber, and the saturable absorber is used for connecting the input end of the saturable absorber. The output end of the body is connected to the input end of the polarization controller, the output end of the polarization controller is connected to the input end of the isolator, the input end of the isolator is connected to the input end of the wavelength division multiplexer, the 1% output end of the extracavity coupler is connected to the feedback system, and the 99% output end of the extracavity coupler is used for the final output; the feedback control system includes an image acquisition module, an image processing module, and a feedback control circuit, the image acquisition module acquires the high-order transverse mode output from the output end of the multi-mode output coupler in the above-mentioned ring laser system; the image processing module converts the acquired image into a digital signal and inputs it into the feedback control circuit; the feedback control circuit generates a feedback control signal according to the input digital signal by setting a threshold, that is, the required high-order transverse mode.

2. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The output wavelength of the laser diode pump source is 976 nm; the wavelength division multiplexer is a 976 / 1064 nm three-port device, with two input ports, one with a central wavelength of 976 nm and one with a central wavelength of 1064 nm, and a common port with a central wavelength of 1064 nm.

3. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The gain optical fiber is a single-mode or multi-mode gain optical fiber, and the total absorption of the gain optical fiber to the pump light is 20 dB.

4. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The high-order transverse mode generating module comprises an n-core multimode optical fiber and a tapered single-mode optical fiber, the multimode optical fiber is used to excite the high-order mode, and the tapered single-mode optical fiber is used to screen out the high-order mode.

5. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The pigtail fiber of the multimode output coupler is a gradient refractive index multimode optical fiber, which realizes the proportional output of different high-order modes.

6. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The saturable absorber is composed of two sections of Hi060 single-mode optical fibers sandwiched between a section of gradient-index multimode optical fiber. The core diameter or length of the gradient-index multimode optical fiber can be changed by a taper machine, thereby changing the saturable absorption characteristics.

7. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The polarization controller is an in-line polarization controller, which can change the polarization state in the cavity by adjusting the upper knob, that is, the rotation angle, so as to control the laser mode field in the optical fiber to obtain a variety of high-order transverse modes.

8. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The isolator is a polarization-independent isolator, which ensures that light runs unidirectionally in the laser.

9. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The image acquisition module adopts a CCD device to acquire the high-order transverse mode image at the output end of the multi-mode output coupler.

10. The all-fiber spatiotemporal mode-locked laser with controllable high-order transverse mode according to claim 1, characterized in that: The feedback control circuit uses FPGA to judge the digital signal output by the digital image processing module, and is connected to the polarization controller in the laser system to generate a feedback signal and adjust the rotation angle to achieve feedback regulation.

Images