A Passive Q-Switched Fiber Laser Based on Microcavity Photothermal Effect

Abstract

The present invention belongs to the field of laser technology, and specifically discloses a passive Q-switching fiber laser based on the optothermal effect of a microcavity. The Q-switching fiber laser uses an optical microcavity (6) as a Q-switching element; wherein, the optical microcavity (6) realizes passive Q-switching based on its own optothermal effect. The present invention first proposes to use the optothermal effect in an optical microcavity to realize a passive Q-switching fiber laser. Compared with the active Q-switching scheme, the present invention significantly reduces the cost and simplifies the system structure; at the same time, compared with the passive Q-switching element using a saturable absorber, the present invention has the advantages of a high damage threshold and a wide working wavelength band when using an optical microcavity as the passive Q-switching element.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and more specifically, relates to a passive Q-switching fiber laser based on the microcavity photothermal effect. Background Art

[0002] Compared with traditional solid-state, gas, and semiconductor lasers, fiber lasers have been widely used in many fields such as laser processing, fiber optic communication, fiber optic sensing, laser medicine, and lidar due to their many advantages such as compact structure, good stability, no need for cooling, high beam quality, high conversion efficiency, and low manufacturing cost. In recent years, fiber lasers even exceed traditional solid-state lasers in some performance indicators. Q-switching technology is divided into two methods: active and passive. Active Q-switching means introducing an active control element to periodically adjust the intracavity loss or optical field, while passive Q-switching uses elements that do not require an external drive to self-adjust the cavity loss or optical field. Compared with the active Q-switching technology, the passive Q-switching technology has the advantages of no need for an external drive source, simple structure, and low cost. The reported passive Q-switching schemes still have some limitations in realizing pulse output, and new materials, new components, and new mechanisms need to be explored.

[0003] Due to the saturable absorption effect and relatively fast recovery time of saturable absorbers, the reported passive Q-switching elements are mainly saturable absorbers, including dyes, semiconductor saturable absorber mirrors, carbon nanotubes, and low-dimensional materials. However, most saturable absorbers are prone to damage or even failure when working at high pulse powers, and low-dimensional materials can only work in specific wavelength bands due to the limitation of the bandgap. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a passive Q-switching fiber laser based on the microcavity photothermal effect, which for the first time uses the photothermal effect of an optical microcavity to adjust the loss of a fiber loop and realizes Q-switched pulse output. The present invention first proposes to use the photothermal effect of an optical microcavity to realize a passive Q-switching fiber laser. Compared with the active Q-switching scheme, the present invention significantly reduces the cost and simplifies the system structure; at the same time, compared with passive Q-switching elements using saturable absorbers, the present invention uses an optical microcavity as a passive Q-switching element, which has the advantages of high damage threshold and wide working wavelength band.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a passive Q-switching fiber laser based on the microcavity photothermal effect, characterized in that the Q-switching fiber laser uses an optical microcavity (6) as a Q-switching element; wherein, the optical microcavity (6) realizes passive Q-switching based on its own photothermal effect.

[0006] As a further preference of the present invention, the optical microcavity (6) is a silica microsphere cavity with a Q value greater than 10 8 , and preferably has a diameter of 100 μm to 600 μm; correspondingly, the output pulse width of the Q-switched fiber laser is of the order of ns.

[0007] As a further preference of the present invention, the Q-switched fiber laser includes a pump source (1), a wavelength division multiplexer (2), a doped fiber (3), a polarization controller (4), an optical circulator (5), an optical microcavity coupling system, and an optical coupler (8) that are connected in sequence to form an optical fiber loop;

[0008] Among them, the optical microcavity coupling system includes an optical microcavity (6) and a corresponding coupling element. The optical microcavity (6) performs optical signal coupling through this coupling element, and can reduce the modes in the optical microcavity (6) from simultaneously participating in forming the optical fiber loop by using the backscattering of the optical microcavity (6); the optical microcavity (6) can periodically adjust the loss of the optical fiber loop by using its own photothermal effect to achieve passive Q-switching;

[0009] Preferably, the coupling element is a micro-nano fiber (7) or an integrated waveguide structure.

[0010] As a further preference of the present invention, the doped fiber is a rare earth element doped fiber.

[0011] As a further preference of the present invention, the doped fiber is an erbium-doped fiber.

[0012] According to another aspect of the present invention, the present invention provides an application of an optical microcavity as a passive Q-switching element in a Q-switched fiber laser, which is characterized in that the optical microcavity (6) adjusts the loss of the fiber ring cavity based on its own photothermal effect to achieve passive Q-switching.

[0013] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention can achieve the following beneficial effects:

[0014] (1) The present invention first proposes to use an optical microcavity as a Q-switching element, and adjusts the loss of the optical fiber loop by using the photothermal effect of the optical microcavity, thereby realizing a passive Q-switched fiber laser. The present invention further expands the application of the existing optical microcavity, using the optical microcavity as a passive Q-switching element. Compared with the passive Q-switching element using a saturable absorber, the present invention using an optical microcavity as a passive Q-switching element has the advantages of a high damage threshold and a wide working wavelength band.

[0015] Optical microcavity is a common element in the field of optics, and is often used in the fields of high-sensitivity sensing, low-threshold lasers, nonlinear optics, etc. Its shapes mainly include microsphere cavity, microbottle cavity, microbubble cavity, microrod cavity, microdisk cavity, microcore toroidal cavity, microring cavity, etc. Optical microcavity can significantly enhance the interaction between light and matter. Optical microcavity has the characteristics of high Q value and small mode volume. Typical materials used to prepare optical microcavity include silicon dioxide, silicon, silicon nitride, aluminum nitride, lithium niobate, calcium fluoride, magnesium fluoride, etc. These materials have the characteristics of high damage threshold and wide working band. The present invention can couple the optical signal into the microcavity through coupling elements such as micro-nano optical fiber or integrated waveguide structure. The optical signal is bound in a highly restricted space and circulates continuously, forming a very high optical power density in the cavity; and as the optical power continues to accumulate, the temperature of the optical microcavity rises based on the photothermal effect, and the refractive index of the material and the size of the microcavity change at this time, thereby causing the drift of the resonance mode and the change of the mode field distribution. The present invention utilizes the photothermal effect of the optical microcavity and uses the optical microcavity as a passive Q-switching element for the first time, thereby expanding the types of passive Q-switching elements and having low cost.

[0016] In the present invention, when the resonant mode of the optical microcavity is aligned with the resonant mode of the fiber ring cavity, the fiber loop is turned on, the fiber ring cavity is in a low-loss state, and laser output is achieved. Since the photothermal effect of the optical microcavity will cause its resonant mode to redshift (photothermal effect will be generated in the optical microcavity during laser transmission), the resonant mode of the microcavity is further mismatched with the resonant mode of the fiber ring cavity. At this time, the fiber loop is disconnected, the fiber ring cavity is in a high-loss state, and laser output cannot be achieved. After the heat in the optical microcavity dissipates, the resonant mode of the optical microcavity is realigned with the resonant mode of the fiber ring cavity, thereby achieving periodic regulation of the fiber ring cavity loss and outputting Q-switched pulses, thereby achieving passive Q-switching.

[0017] (2) Based on the present invention, a fiber laser can be combined with an optical microcavity, for example, by using a microcavity with a diameter of hundreds of micrometers (e.g., 100 μm to 600 μm) and a Q value greater than 10 8 The silica microsphere cavity realizes passively Q-switched pulse fiber laser with a repetition rate of hundreds of kHz and a pulse width of less than hundreds of nanoseconds.

[0018] (3) In addition, based on the idea of using an optical microcavity as a Q-switching element in the present invention, when other conditions are the same, when the Q value of the optical microcavity is higher, the repetition frequency of the obtained Q-switched pulse is higher and the pulse width is narrower; conversely, when the Q value of the optical microcavity is lower, the repetition frequency of the obtained Q-switched pulse is lower and the pulse width is wider.

[0019] In summary, the passively Q-switched fiber laser based on the microcavity photothermal effect of the present invention has the advantages of simple structure, high damage threshold, wide operating band, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of the passive Q - switched fiber laser in the present invention.

[0021] Figure 2 It is the Q - switched pulse output of Example 1; among them, Figure 2 (a) in corresponds to the measured data, Figure 2 (b) in then compares the measured data with the fitted data.

[0022] Figure 3 It is the Q - switched pulse output of Example 2; among them, Figure 3 (a) in corresponds to the measured data, Figure 3 (b) in then compares the measured data with the fitted data.

[0023] Figure 1 The meanings of the reference numerals in the figures are as follows: 1 is a pump source; 2 is a wavelength - division multiplexer; 3 is a doped fiber; 4 is a polarization controller; 5 is an optical circulator; 6 is an optical micro - cavity; 7 is a micro - nano fiber; 8 is an optical coupler. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Example 1

[0026] The schematic structural diagram of the passive Q - switched fiber laser is as Figure 1 shown. A 980 - nm laser is used as the pump source 1; a 980 / 1550 - nm wavelength - division multiplexer 2 is used to couple the 980 - nm pump light into the fiber loop; a 1 - m - long erbium - doped fiber 3 is used as the gain medium; a polarization controller 4 is used to adjust the polarization state of the light; an optical circulator 5 (when an optical signal is input from any port, it will output from the next port in the digital order I, II, III) ensures the unidirectional transmission of the optical signal in the loop and re - inputs the light signal backscattered by the micro - cavity into the fiber loop; a micro - nano fiber 7 is used to couple with the optical micro - cavity 6. The micro - nano fiber 7 is prepared by the fused - biconical taper method and has a diameter of 1.2 μm; an optical coupler 8 couples part of the light out of the fiber loop as the output light. In this embodiment, a silica micro - sphere cavity with a diameter of 213 μm and a Q - value of 1.1×10 8 is used as the optical micro - cavity 6, and the Q - switched pulse generated thereby is as Figure 2 shown. The repetition frequency of the Q - switched pulse is 653 kHz, and the pulse width is 25.8 ns (wherein, Figure 2(The fitting curve in (b) is obtained by fitting with a Gaussian function).

[0027] Example 2

[0028] The structural schematic diagram of the passively Q-switched fiber laser is similar to that in Example 1. In this example, a silica microsphere cavity with a diameter of 167 μm and a Q value of 3×10 7 is used as the optical microcavity 6, and the Q-switched pulses generated thereby are as Figure 3 shown. The repetition rate of the Q-switched pulses is 215 kHz, and the pulse width is 1.46 μs (wherein, Figure 3 (The fitting curve in (b) is obtained by fitting with a Gaussian function).

[0029] The above embodiments are only examples. For example, in addition to using a silica microsphere cavity, optical microcavities with other shapes, materials, and Q values can also be used according to actual needs; for another example, in addition to coupling through the micro-nano fiber 7, an integrated waveguide structure coupling or a spatial optical coupling method known in the prior art can also be used.

[0030] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A passive Q-switching fiber laser based on the microcavity optothermal effect, characterized in that, The Q-switched fiber laser uses an optical microcavity (6) as a Q-switching element; wherein, the optical microcavity (6) realizes passive Q-switching based on its own photothermal effect. The optical microcavity (6) is a silica microsphere cavity with a Q value greater than 10 8 , and the diameter is 100 μm to 600 μm; correspondingly, the output pulse width of the Q-switched fiber laser is of the order of ns; The Q-switched fiber laser includes a pump source (1), a wavelength division multiplexer (2), a doped fiber (3), a polarization controller (4), an optical circulator (5), an optical microcavity coupling system, and an optical coupler (8) that are connected in sequence to form an optical fiber loop. Among them, the optical microcavity coupling system includes an optical microcavity (6) and a corresponding coupling element. The optical microcavity (6) couples optical signals through this coupling element, and can use the backscattering of the optical microcavity (6) to reduce the modes in the optical microcavity (6) from simultaneously participating in forming the optical fiber loop; the optical microcavity (6) can periodically adjust the loss of the optical fiber loop using its own photothermal effect to achieve passive Q-switching.

2. The passive Q-switching fiber laser based on the microcavity optothermal effect according to claim 1, characterized in that The coupling element is a micro-nano fiber (7) or an integrated waveguide structure.

3. The passive Q-switching fiber laser based on the microcavity optothermal effect according to claim 1, wherein The doped fiber is a rare earth element doped fiber.

4. The passive Q-switched fiber laser based on the microcavity photothermal effect according to claim 3, characterized in that, The doped fiber is an erbium-doped fiber.

5. Use of the passive Q-switching fiber laser based on the microcavity optothermal effect according to any one of claims 1-4 as a Q-switching fiber laser, wherein, The optical microcavity (6) adjusts the loss of the optical fiber loop cavity based on its own photothermal effect to achieve passive Q-switching.

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