A passively mode-locked fiber laser with switchable transverse mode and an optical communication system

Abstract

This invention discloses a passively mode-locked fiber laser with switchable transverse modes and an optical communication system, relating to the field of ultrafast optical technology. The passively mode-locked fiber laser comprises a pump source and a laser resonator. The laser resonator comprises a wavelength division multiplexer, a gain fiber, a few-mode isolator, a first polarization controller, a saturable absorber, a second polarization controller, a mode-selective photon lantern, and a few-mode coupler, all connected in sequence along the direction of light propagation. Compared to existing technologies, the present invention offers low insertion loss and high spatial mode selection flexibility, making it widely applicable in communications, industrial processing, detection, and other fields.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast optical technology, and more particularly to a transverse-mode switchable passively mode-locked fiber laser and an optical communication system. Background Art

[0002] Currently, spatiotemporally mode-locked fiber lasers have attracted widespread attention in the field of ultrafast optics. These ultrashort-pulse fiber lasers support simultaneous locking of both transverse and longitudinal modes, generating complex nonlinear dynamic effects within the resonant cavity. This approach is of great significance for the study of nonlinearities in optical fibers.

[0003] Spatiotemporally mode-locked fiber lasers can simultaneously lock multiple transverse modes, but research on lasers generating switchable transverse modes is currently scarce. A transverse mode is a spatial distribution of the electromagnetic field of a light wave across the cross-section of an optical fiber. Transverse mode switchability, which allows mode-locked pulses to be output in different transverse modes within the same laser, allows switching from one transverse mode to another, such as from the fundamental mode to a higher-order mode, or vice versa, and has broad application prospects.

[0004] The spot of the fundamental mode laser is usually circular, while the spot of the high-order mode laser is usually multi-lobed. Due to its greater information content and degree of freedom, high-order modes have been widely used in many aspects. Existing technologies have been used to generate high-order modes, including the use of offset fusion, long-period fiber gratings, acoustic fiber gratings, few-mode fiber Bragg gratings, and mode selective couplers. Among them, the scheme using offset fusion technology to excite high-order modes cannot switch the high-order mode pulses generated by it; most of the schemes using fiber gratings can only generate one transverse mode, and a small number can generate different modes at different wavelengths, but they rely on the reflection spectrum of the fiber grating, and the switching of transverse modes is greatly limited; the scheme using a single mode selective coupler can only achieve the output of a single high-order mode, and the scheme of connecting multiple mode selective couplers in series can achieve the output of multiple transverse modes, but the insertion loss is large. Summary of the Invention

[0005] In order to overcome the defects of large insertion loss and large limitation in the prior art of realizing transverse mode switchability, the present invention provides a transverse mode switchable passively mode-locked fiber laser and an optical communication system.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0007] In a first aspect, a transverse-mode switchable passively mode-locked fiber laser comprises: a pump source and a laser resonant cavity; the laser resonant cavity comprises a wavelength division multiplexer, a gain fiber, a few-mode isolator, a first polarization controller, a saturable absorber, a second polarization controller, a mode-selective photon lantern, and a few-mode coupler, which are sequentially connected along the light propagation direction;

[0008] The pump light emitted by the pump source is combined by the wavelength division multiplexer and then generates stimulated emission light through the gain fiber. The stimulated emission light is sequentially passed through the few-mode isolator, the first polarization controller, the saturable absorber and the second polarization controller for polarization state adjustment and mode locking, and then undergoes transverse mode switching through the mode-selective photon lantern.

[0009] In which, the stimulated radiation light circulates back and forth in the laser resonant cavity until the intensity of the stimulated radiation light reaches a preset laser oscillation threshold, and then outputs pulsed laser through the few-mode coupler; the first port of the few-mode coupler is connected to the output end of the mode-selective photon lantern, the second port of the few-mode coupler is connected to the signal end of the wavelength division multiplexer, and the third port of the few-mode coupler is used to output pulsed laser.

[0010] As a preferred technical means, the gain fiber is an erbium-doped fiber.

[0011] As a preferred technical means, the pump source is a single-mode output.

[0012] Furthermore, the output wavelength of the pump source is 974nm-980nm or 1460nm-1490nm.

[0013] As a preferred technical means, the wavelength division multiplexer is a few-mode wavelength division multiplexer.

[0014] As a preferred technical means, the first polarization controller and / or the second polarization controller is a manual squeezing polarization controller or a three-ring polarization controller.

[0015] As a preferred technical means, the modulation depth of the saturable absorber is 2%-55%.

[0016] As a preferred technical means, the coupling ratio of the few-mode coupler is 95:5, 90:10, 80:20 or 70:30.

[0017] As an optimal technical means, the mode-selective photon lantern is a three-mode selective photon lantern or a six-mode selective photon lantern.

[0018] In a second aspect, an optical communication system includes the passively mode-locked fiber laser described in the first aspect.

[0019] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0020] This invention proposes a passively mode-locked fiber laser with switchable transverse modes and an optical communication system. The passively mode-locked fiber laser uses a saturable absorber as the mode-locking device and employs a mode-selective photon lantern to excite higher-order modes. Through the coordination of these devices, multiple conversions are achieved within the cavity, enabling mode-locked ultrashort pulse output from the passively mode-locked fiber laser with switchable transverse modes. Compared to existing technologies, this invention offers low insertion loss and high flexibility in spatial mode selection, making it widely applicable in communications, industrial processing, detection, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the passively mode-locked fiber laser according to Example 1 of the present invention;

[0022] Figure 2 The passively mode-locked fiber laser fundamental mode LP of embodiment 1 of the present invention 01 Schematic diagram of the output mode field intensity distribution;

[0023] Figure 3 The passively mode-locked fiber laser fundamental mode LP of embodiment 1 of the present invention 01 Output pulse sequence diagram;

[0024] Figure 4 The passively mode-locked fiber laser high-order mode LP of embodiment 1 of the present invention 11a Schematic diagram of the output mode field intensity distribution;

[0025] Figure 5 The passively mode-locked fiber laser high-order mode LP of embodiment 1 of the present invention 11a Output pulse sequence diagram;

[0026] Figure 6 The passively mode-locked fiber laser high-order mode LP of embodiment 1 of the present invention 11b Schematic diagram of the output mode field intensity distribution;

[0027] Figure 7 The passively mode-locked fiber laser high-order mode LP of embodiment 1 of the present invention 11b Output pulse sequence diagram; in the attached figure, the components represented by each number are listed as follows:

[0028] 1- pump source; 2- wavelength division multiplexer; 3- gain fiber; 4- few-mode isolator; 5- first polarization controller; 6- saturable absorber; 7- second polarization controller; 8- mode-selective photon lantern; 9- few-mode coupler. DETAILED DESCRIPTION

[0029] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances, and this is merely a way of distinguishing the objects of the same attributes when describing them in the embodiments of the present application. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, so that the process, method, system, product or equipment comprising a series of units need not be limited to those units, but may include other units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0030] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent;

[0031] In order to better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size;

[0032] It is understandable to those skilled in the art that some well-known structures and descriptions thereof may be omitted in the drawings.

[0033] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0034] Example 1

[0035] This embodiment proposes a passively mode-locked fiber laser with switchable transverse mode. Figure 1 , comprising: a pump source 1 and a laser resonant cavity; the laser resonant cavity comprises a wavelength division multiplexer 2, a gain fiber 3, a few-mode isolator 4, a first polarization controller 5, a saturable absorber 6, a second polarization controller 7, a mode-selective photon lantern 8 and a few-mode coupler 9, which are sequentially connected along the light propagation direction;

[0036] The pump light emitted by the pump source 1 is combined by the wavelength division multiplexer 2 and then generates stimulated emission light through the gain fiber 3. The stimulated emission light is sequentially passed through the few-mode isolator 4, the first polarization controller 5, the saturable absorber 6 and the second polarization controller 7 for polarization state adjustment and mode locking, and then undergoes transverse mode switching through the mode selective photon lantern 8;

[0037] In which, the stimulated radiation light circulates back and forth in the laser resonant cavity until the intensity of the stimulated radiation light reaches a preset laser oscillation threshold, and is then output as a pulsed laser through the few-mode coupler 9; the first port of the few-mode coupler 9 is connected to the output end of the mode-selective photon lantern 8, the second port of the few-mode coupler 9 is connected to the signal end of the wavelength division multiplexer 2, and the third port of the few-mode coupler 9 is used to output pulsed laser.

[0038] Those skilled in the art should understand that, in this embodiment, the pump source 1 is connected to the pump input end of the wavelength division multiplexer 2; one end of the gain fiber 3 is connected to the common end of the wavelength division multiplexer 2, and the other end is connected to the input end of the few-mode isolator 4; one end of the first polarization controller 5 is connected to the output end of the few-mode isolator 4, and the other end is connected to one end of the saturable absorber 6; the other end of the saturable absorber 6 is connected to one end of the second polarization controller 7; the input end of the mode-selective photon lantern 8 is connected to the other end of the second polarization controller 7.

[0039] It should be noted that the laser resonator is a ring loop, and the pulsed laser is generated through multiple cycles within the ring loop. The pump source 1 is used to emit pump light. After the pump light is combined with the signal light in the wavelength division multiplexer 2, the pump light in the gain fiber 3 provides energy for amplifying the signal light, achieving gain amplification of the signal light and generating stimulated emission light. The few-mode isolator 4 is used to prevent the stimulated emission light from reflecting within the laser resonator. The first polarization controller 5 and the second polarization controller 7 are used to adjust the polarization state. The saturable absorber 6 is used for mode locking. The mode-selective photon lantern 8 is used to achieve transverse mode switching. Compared to existing technologies, the passively mode-locked fiber laser described in this embodiment has a compact structure, high integration, low insertion loss, high flexibility in spatial mode selection, and high stability in the output pulsed laser. In addition, this embodiment adopts an all-fiber structure without the presence of spatial optical elements, which has the advantages of small size and low energy consumption. It can be widely used in communications, industrial processing, detection and other fields.

[0040] In addition, in this embodiment, the wavelength division multiplexer 2 is a fused-taper fiber type wavelength division multiplexer.

[0041] In some examples, the mode-selective photonic lantern 8 has a few-mode output.

[0042] In some examples, the gain fiber 3 is a few-mode gain fiber;

[0043] In other examples, the gain fiber 3 is a multimode gain fiber.

[0044] In a preferred embodiment, the gain fiber 3 is an erbium-doped fiber.

[0045] In some examples, the gain fiber 3 is a few-mode erbium-doped fiber.

[0046] In a preferred embodiment, the pump source 1 is a single-mode output.

[0047] In some examples, the pump source 1 is a 976 nm laser with single-mode output.

[0048] In an optional embodiment, the output wavelength of the pump source 1 is 974nm-980nm or 1460nm-1490nm.

[0049] It should be noted that the output wavelength of the pump source 1 is set by those skilled in the art according to actual conditions.

[0050] In some examples, the output wavelength of the pump source 1 is 974 nm;

[0051] In some examples, the output wavelength of the pump source 1 is 976 nm;

[0052] In some examples, the output wavelength of the pump source 1 is 980 nm;

[0053] In some examples, the output wavelength of the pump source 1 is 1460 nm;

[0054] In some examples, the output wavelength of the pump source 1 is 1480 nm;

[0055] In other examples, the output wavelength of the pump source 1 is 1490 nm.

[0056] In a preferred embodiment, the wavelength division multiplexer 2 is a few-mode wavelength division multiplexer.

[0057] In a preferred embodiment, the first polarization controller 5 and / or the second polarization controller 7 is a manual squeeze-type polarization controller or a three-ring polarization controller.

[0058] In some examples, the first polarization controller 5 is a manual squeeze-type polarization controller;

[0059] In some examples, the second polarization controller 7 is a manual squeeze-type polarization controller;

[0060] In some other examples, both the first polarization controller 5 and the second polarization controller 7 are manual squeezing polarization controllers.

[0061] In some examples, the first polarization controller 5 is a three-ring polarization controller;

[0062] In some examples, the second polarization controller 7 is a three-ring polarization controller;

[0063] In some other examples, both the first polarization controller 5 and the second polarization controller 7 are three-ring polarization controllers.

[0064] In a preferred embodiment, the modulation depth of the saturable absorber 6 is 2%-55%.

[0065] In some examples, the modulation depth of the saturable absorber 6 is 2%;

[0066] In some examples, the modulation depth of the saturable absorber 6 is 7%;

[0067] In some examples, the modulation depth of the saturable absorber 6 is 25%;

[0068] In some examples, the modulation depth of the saturable absorber 6 is 30%;

[0069] In some other examples, the modulation depth of the saturable absorber 6 is 55%.

[0070] In an optional embodiment, the relaxation time of the saturable absorber 6 is 2 ps-12 ps.

[0071] In some examples, the relaxation time of the saturable absorber 6 is 2 ps;

[0072] In some examples, the relaxation time of the saturable absorber 6 is 6 ps;

[0073] In some examples, the relaxation time of the saturable absorber 6 is 10 ps;

[0074] In some other examples, the relaxation time of the saturable absorber 6 is 12 ps.

[0075] Those skilled in the art should understand that the few-mode coupler 9 is an all-fiber device. Compared with spatial optical elements, all-fiber structure devices have the advantages of small size, low energy consumption, long life, high stability, and maintenance-free.

[0076] It should be noted that the coupling ratio of the few-mode coupler 9 is set by those skilled in the art according to actual conditions.

[0077] In a preferred embodiment, the coupling ratio of the few-mode coupler 9 is 95:5, 90:10, 80:20 or 70:30.

[0078] In some examples, the second port of the few-mode coupler 9 is a 90% output port, and the third port is a 10% output port.

[0079] Those skilled in the art should understand that the stimulated emission light outputted from the second port is inputted into the signal end of the wavelength division multiplexer 2 as signal light.

[0080] In a preferred embodiment, the mode-selective photon lantern 8 is a three-mode selective photon lantern or a six-mode selective photon lantern.

[0081] In some examples, the mode-selective photon lantern 8 is a three-mode selective photon lantern;

[0082] In some examples, the mode-selective photon lantern 8 is a six-mode selective photon lantern;

[0083] In other examples, the mode-selective photonic lantern 8 can be replaced with a mode-selective device that supports a greater number of modes, such as a mode-selective coupler, an optical plane converter, and the like.

[0084] This embodiment also analyzes the pulse laser output by the passively mode-locked fiber laser to verify the switchability and stability of the transverse mode of its pulse output. A 976nm laser is used as the pump source, and the transverse mode of the output pump light is the fundamental mode LP. 01 :

[0085] (1) Based on the basic model LP 01 The mode-locked output has a mode field intensity distribution as shown below: Figure 2 As shown, with fundamental mode LP 01 The central light field distribution characteristics of the time domain pulse sequence are as follows: Figure 3 As shown;

[0086] (2) High-order mode LP 11a The mode-locked output has a mode field intensity distribution as shown below: Figure 4 As shown, it has high-order mode LP 11a The symmetrical light field distribution characteristics, its time domain pulse sequence is as follows Figure 5 As shown;

[0087] (3) High-order mode LP 11b The mode-locked output has a mode field intensity distribution as shown below: Figure 6 As shown, it has high-order mode LP 11b Symmetrical light field distribution characteristics and high-order mode LP 11a It has vertical light field distribution characteristics, and its time domain pulse sequence is as follows Figure 7 shown.

[0088] Example 2

[0089] This embodiment provides a light source including the passively mode-locked fiber laser described in Embodiment 1.

[0090] It can be understood that the options in the above embodiment 1 are also applicable to this embodiment, so they will not be described again here.

[0091] Example 3

[0092] This embodiment provides an optical communication system, including a passively mode-locked fiber laser, wherein the passively mode-locked fiber laser includes a 976 nm laser with single-mode output and a laser resonant cavity; the laser resonant cavity includes a few-mode wavelength division multiplexer, a few-mode erbium-doped gain fiber, a few-mode isolator 4, a first polarization controller 5, a saturable absorber 6, a second polarization controller 7, a three-mode mode-selective photon lantern, and a few-mode coupler 9, which are sequentially connected along the light propagation direction;

[0093] The pump light emitted by the 976nm laser as a pump source is combined by the few-mode wavelength division multiplexer and then passes through the few-mode erbium-doped gain fiber to generate stimulated emission light. The stimulated emission light then passes through the few-mode isolator 4, the first polarization controller 5, the saturable absorber 6, and the second polarization controller 7 in sequence, and then undergoes polarization state adjustment and mode locking to obtain a pulsed laser. The pulsed laser is then switched to a transverse mode by the three-mode mode-selective photon lantern and outputs a pulsed laser through the few-mode coupler 9.

[0094] Among them, the first port of the few-mode coupler 9 is connected to the output end of the three-mode selective photon lantern, the second port of the few-mode coupler 9 is connected to the signal end of the few-mode wavelength division multiplexer, and the third port of the few-mode coupler 9 is used to output pulsed laser.

[0095] In some examples, the optical communication system operates in a band within the 1.5 μm range.

[0096] It can be understood that the options in the above embodiment 1 are also applicable to this embodiment, so they will not be described again here.

[0097] The same or similar reference numerals correspond to the same or similar components;

[0098] The terms used in the drawings to describe positional relationships are for illustrative purposes only and should not be construed as limiting this patent;

[0099] Obviously, 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 can 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 shall be included within the scope of protection of the claims of the present invention.

Claims

1. A passively mode-locked fiber laser with switchable transverse mode, characterized in that: include: A pump source (1) and a laser resonant cavity; the laser resonant cavity comprises a wavelength division multiplexer (2), a gain optical fiber (3), a few-mode isolator (4), a first polarization controller (5), a saturable absorber (6), a second polarization controller (7), a mode-selective photon lantern (8), and a few-mode coupler (9) connected in sequence along a light propagation direction; the wavelength division multiplexer (2) is a few-mode wavelength division multiplexer; The pump light emitted by the pump source (1) is combined by the wavelength division multiplexer (2) and then generates stimulated radiation light through the gain fiber (3). The stimulated radiation light is sequentially passed through the few-mode isolator (4), the first polarization controller (5), the saturable absorber (6) and the second polarization controller (7) for polarization state adjustment and mode locking, and then is switched to a transverse mode by the mode-selective photon lantern (8); The stimulated radiation light circulates back and forth in the laser resonant cavity until the intensity of the stimulated radiation light reaches a preset laser oscillation threshold, and then is output as a pulsed laser through the few-mode coupler (9); the first port of the few-mode coupler (9) is connected to the output end of the mode-selective photon lantern (8), the second port of the few-mode coupler (9) is connected to the signal end of the wavelength division multiplexer (2), and the third port of the few-mode coupler (9) is used to output the pulsed laser.

2. The passively mode-locked fiber laser with switchable transverse mode according to claim 1, characterized in that: The gain optical fiber (3) is an erbium-doped optical fiber.

3. The passively mode-locked fiber laser with switchable transverse mode according to claim 1, characterized in that: The pump source (1) is a single-mode output.

4. The passively mode-locked fiber laser with switchable transverse mode according to claim 3, characterized in that: The output wavelength of the pump source (1) is 974nm-980nm or 1460nm-1490nm.

5. The passively mode-locked fiber laser with switchable transverse mode according to claim 1, characterized in that: The first polarization controller (5) and / or the second polarization controller (7) is a manual squeezing polarization controller or a three-ring polarization controller.

6. The passively mode-locked fiber laser with switchable transverse mode according to claim 1, characterized in that: The modulation depth of the saturable absorber (6) is 2%-55%.

7. The passively mode-locked fiber laser with switchable transverse mode according to claim 1, characterized in that: The coupling ratio of the few-mode coupler (9) is 95:5, 90:10, 80:20 or 70:

30.

8. A transverse mode switchable passively mode-locked fiber laser according to any one of claims 1 to 7, characterized in that: The mode-selective photon lantern (8) is a three-mode selective photon lantern or a six-mode selective photon lantern.

9. An optical communication system, characterized in that: The passively mode-locked fiber laser comprises the passively mode-locked fiber laser according to any one of claims 1 to 8.

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