阅读说明：本技术 一种全光纤色散调节方法及全光纤色散管理器件 (All-fiber dispersion adjusting method and all-fiber dispersion management device ) 是由 王屹山 赵卫 王虎山 张挺 潘然 胡晓鸿 张伟 于 2020-05-28 设计创作，主要内容包括：本发明提供了一种全光纤色散调节方法及全光纤色散管理器件,该器件利用大角度倾斜光纤光栅的模式耦合作用特性以及光纤高阶模式的色散特性,实现高性能的全光纤色散管理,对于超快光纤激光技术的实用化发展具有推动作用。本发明基于大角度倾斜光纤光栅的全光纤色散管理器件包括沿光传输方向依次连接的第一大角度倾斜光纤光栅、传输光纤和第二大角度倾斜光纤光栅；其中,第一大角度倾斜光纤光栅和第二大角度倾斜光纤光栅的倾斜角度为66～89度,所述传输光纤为单模光纤、少量模光纤或多模光纤。(The invention provides an all-fiber dispersion adjusting method and an all-fiber dispersion management device, which utilize the mode coupling action characteristic of a large-angle inclined fiber grating and the dispersion characteristic of a high-order mode of an optical fiber to realize high-performance all-fiber dispersion management and have a promoting effect on the practical development of an ultrafast fiber laser technology. The all-fiber dispersion management device based on the large-angle inclined fiber grating comprises a first large-angle inclined fiber grating, a transmission fiber and a second large-angle inclined fiber grating which are sequentially connected along the light transmission direction; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees, and the transmission fiber is a single-mode fiber, a small-number-mode fiber or a multi-mode fiber.)

1. An all-fiber dispersion adjustment method, comprising: when light transmitted in the fiber core of the optical fiber passes through the first large-angle inclined fiber grating, the light is coupled into the fiber cladding of the single-mode fiber and transmitted in a high-order mode; coupling the fiber cladding to the fiber core for continuous transmission when passing through the second large-angle inclined fiber grating; the adjustment of the dispersion amount is realized by controlling the length of the single-mode fiber; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees.

2. An all-fiber dispersion adjustment method, comprising: the light transmitted in the fiber core is coupled to the fiber core or the fiber cladding of a few-mode fiber or a multimode fiber and transmitted in a high-order mode when passing through the first large-angle inclined fiber grating, and is coupled back to the fiber core basic mode from the fiber core high-order mode or the fiber cladding for continuous transmission when passing through the second large-angle inclined fiber grating; the dispersion amount is adjusted by controlling the length of a small number of mode fibers or multimode fibers; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees.

3. The utility model provides an all-fiber dispersion management device based on wide-angle slope fiber grating which characterized in that: the fiber grating comprises a first large-angle inclined fiber grating, a transmission fiber and a second large-angle inclined fiber grating which are sequentially connected along the light transmission direction; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees, and the transmission fiber is a single-mode fiber, a small-number-mode fiber or a multi-mode fiber.

4. The all-fiber dispersion management device based on large-angle tilted fiber grating as claimed in claim 3, wherein: the inclination directions of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are the same or opposite along the axial direction of the optical fiber.

5. The all-fiber dispersion management device based on large-angle tilted fiber grating as claimed in claim 3 or 4, wherein: the first large-angle inclined fiber grating and the second large-angle inclined fiber grating have the same inclination angle.

6. The all-fiber dispersion management device based on large-angle tilted fiber gratings of claim 5, wherein: the grating periods of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are the same.

7. The all-fiber dispersion management device based on large-angle tilted fiber gratings of claim 6, wherein: the first large-angle inclined fiber grating, the transmission fiber and the second large-angle inclined fiber grating are manufactured on the same fiber, or are manufactured respectively and then are subjected to fiber fusion.

8. The all-fiber dispersion management device based on large-angle tilted fiber gratings of claim 7, wherein: and low-folding glue is coated on the fiber cladding of the transmission fiber.

9. An ultrashort pulse fiber laser is characterized in that: the all-fiber dispersion management device based on large-angle tilted fiber grating of any of claims 3 to 8, wherein the all-fiber dispersion management device based on large-angle tilted fiber grating is fused in the fiber laser cavity to provide quantitative dispersion and realize the management of net dispersion in the fiber laser cavity.

10. An ultrashort pulse fiber laser is characterized in that: the all-fiber dispersion management device based on the large-angle tilted fiber grating, which comprises any one of claims 3 to 8, is welded at the output fiber end of the laser to realize the compression or broadening of the ultrashort pulse laser.

Technical Field

The invention relates to the field of optical fiber devices and optical fiber lasers, in particular to an all-fiber dispersion adjusting method and an all-fiber dispersion management device.

Background

The fiber laser has unique technical advantages of high beam quality, high efficiency, high integration, high reliability and the like, and becomes an important development direction in the technical field of laser. The ultrashort pulse fiber laser has the remarkable characteristics of narrow pulse width, high repetition frequency, high peak power, wide spectral range and the like, and has wide application and huge market value in the fields of precision machining, medicine, high-speed imaging, strong-field physics, precision measurement, optical fiber sensing and the like.

In fiber ultrashort pulse lasers, especially in femtosecond laser technology, dispersion management is a major physical problem and key technology. Dispersion in optical media is the phenomenon that the phase and group velocities of light propagate in a transparent medium as a function of frequency. The dispersion characteristics have a significant effect on the transmission of the pulses, since the pulses have a spectral width range and therefore cause the frequency components to be transmitted at different speeds. In the case of normal dispersion, the group velocity is smaller in the high frequency part, thus producing positive chirp, while anomalous dispersion produces negative chirp. Having the opposite amount of dispersion as the pulses may be used to compress the pulses, while having the same amount of dispersion as the pulses may be used to broaden the pulses. Therefore, dispersion management is of great significance for realizing stable and reliable ultrashort pulse laser.

The wide-range and accurate full-fiber dispersion management is difficult to realize, especially in the wave band below 1.3 microns, the fundamental mode light in the ordinary fiber is in a positive dispersion region, and negative dispersion compensation and management are needed to be provided for obtaining narrow ultrashort pulses. Three conventional dispersion management devices that are commonly used today and have the following problems: (1) diffraction grating, the principle of which is that when light pulse is incident on one grating of two mutually parallel grating pairs, the angles at which different frequency components in the pulse are diffracted are notSimilarly, when the pulse reaches the second grating, each frequency component is subjected to a different time delay, and dispersion management can be achieved. However, the dispersion device has large space occupancy, destroys the full optical fiber structure, and causes the problems of large loss, complex structure, difficult adjustment and the like; (2) the photonic crystal fiber has a cladding air hole structure, so that the refractive index difference between the fiber core and the cladding is increased, and the waveguide dispersion can present anomalous dispersion characteristics, thereby being used for dispersion compensation. However, the hollow structure of the photonic crystal fiber is easy to cause optical feedback, which affects the stability of the mode locking, and the fusion loss of the photonic crystal fiber and the common fiber is high due to difficult fusion; (3) the chirped fiber grating has grating period varying axially along the fiber core, different grating periods corresponding to different Bragg reflecting wavelengths, and short wavelength and long wavelength components with time delay difference to realize dispersion management. The chirped fiber grating needs to be shaped by an apodization technology, and needs to be matched with a circulator to be used in a ring cavity fiber laser. In addition, the amount of dispersion compensation typically required in ultrafast fiber lasers is small (typically only 0.01-1 ps)²) To realize such compensation of small dispersion and a large spectral response range, a large amount of chirp (generally greater than 80 nm/cm) is required for the fiber grating, and the conventional fiber grating manufacturing process based on the phase mask method cannot realize such a large amount of chirp, so that the chirped fiber grating usually introduces excessive dispersion, and cannot realize precise management of small dispersion. In recent years, the chirped fiber grating with large chirp quantity and small dispersion can be realized by adopting a special optical path design, but the reflectivity of the chirped fiber grating is generally less than 20%, and large loss can be introduced into a ring cavity ultrashort pulse laser.

Disclosure of Invention

In order to solve the problems existing in the background technology, the invention provides an all-fiber dispersion adjusting method and an all-fiber dispersion management device, the device utilizes the mode coupling action characteristic of a large-angle inclined fiber grating and the dispersion characteristic of a high-order mode of an optical fiber to realize high-performance all-fiber dispersion management, and the device has a promoting effect on the practical development of an ultrafast fiber laser technology.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a full optical fiber dispersion adjustment method, light transmitted in an optical fiber core is coupled to an optical fiber cladding of a single mode fiber to be transmitted in a high-order mode when passing through a first large-angle inclined optical fiber grating; coupling the fiber cladding to the fiber core for continuous transmission when passing through the second large-angle inclined fiber grating; the adjustment of the dispersion amount is realized by controlling the length of the single-mode fiber; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees.

The invention also provides another full-fiber dispersion adjusting method, wherein light transmitted in the fiber core is coupled to the fiber core or the fiber cladding of a few-mode fiber or multimode fiber and transmitted in a high-order mode when passing through a first large-angle inclined fiber grating, and is coupled back to the fiber core basic mode from the fiber core high-order mode or the fiber cladding for continuous transmission when passing through a second large-angle inclined fiber grating; the dispersion amount is adjusted by controlling the length of a small number of mode fibers or multimode fibers; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees.

Meanwhile, the invention also provides an all-fiber dispersion management device based on the large-angle inclined fiber grating, which comprises a first large-angle inclined fiber grating, a transmission fiber and a second large-angle inclined fiber grating which are sequentially connected along the light transmission direction; the inclination angles of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are 66-89 degrees, and the transmission fiber is a single-mode fiber, a small-number-mode fiber or a multi-mode fiber.

Further, the inclination directions of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are the same or opposite along the axial direction of the optical fiber.

Further, the first large-angle inclined fiber grating and the second large-angle inclined fiber grating have the same inclination angle.

Further, the grating periods of the first large-angle inclined fiber grating and the second large-angle inclined fiber grating are the same.

Furthermore, the first large-angle inclined fiber grating, the transmission fiber and the second large-angle inclined fiber grating are manufactured on the same fiber, or are manufactured respectively and then are subjected to fiber fusion.

Further, the fiber cladding of the transmission fiber is coated with low-folding glue.

In addition, the invention also provides an ultrashort pulse optical fiber laser, which comprises the full-optical-fiber dispersion management device based on the large-angle inclined optical fiber grating, wherein the full-optical-fiber dispersion management device based on the large-angle inclined optical fiber grating is welded in the optical fiber laser cavity to provide quantitative dispersion and realize the management of net dispersion in the optical fiber laser cavity.

The invention also provides another ultrashort pulse fiber laser which comprises the all-fiber dispersion management device based on the large-angle inclined fiber grating, wherein the all-fiber dispersion management device based on the large-angle inclined fiber grating is welded at the output fiber end of the laser to realize the compression or broadening of the ultrashort pulse laser.

Compared with the prior art, the invention has the following technical effects:

1. the invention adopts the large-angle inclined fiber grating to realize the optical coupling of different modes in the optical fiber, so that the all-fiber dispersion management device has the following advantages: (a) compared with the traditional mode coupling modes such as stress extrusion, bending, dislocation welding and the like, the mode coupling in the optical fiber realized by the large-angle inclined fiber grating can have higher precision and coupling efficiency; (b) the large-angle inclined fiber grating is of an all-fiber structure, and has higher system integration level and reliability for the fiber laser; (c) compared with a long-period fiber grating, the large-angle inclined fiber grating has polarization response, and the polarization degree of output laser can be improved; (d) two large-angle inclined fiber gratings can be respectively designed and optimized, different coupling efficiency and response bandwidth are realized, and further parameters of devices are easier to optimize.

2. The invention adopts the fiber high-order mode dispersion characteristic to carry out dispersion management, so that the all-fiber dispersion management device has the following advantages: (a) the high-order mode dispersion coefficient range is large, and the method is suitable for an ultrashort pulse laser seed source and a system needing pulse broadening, such as a chirped pulse amplification system; (b) the negative dispersion of the wave band below 1.3 microns is easy to realize, and the method has a remarkable effect on the generation of femtosecond laser with the wave band of 1 micron; (c) after the coupling mode is determined, the adjustment of the dispersion amount can be simply realized by controlling the length of the transmission optical fiber; (d) the fiber cladding and the few-mode or multi-mode fiber core have large mode field area and high nonlinear threshold, and can bear higher power.

Drawings

FIG. 1 is a schematic diagram of a dispersion management device based on a large-angle tilted fiber grating according to the present invention (the fiber is a single-mode fiber);

FIG. 2 is a schematic diagram of a dispersion management device based on a large-angle tilted fiber grating according to the present invention (the fiber is a few-mode fiber or a multimode fiber);

fig. 3 is a schematic diagram of a dispersion management device based on a large-angle tilted fiber grating according to the present invention (two large-angle tilted fiber gratings have opposite grating tilt directions).

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

The invention provides a dispersion management device based on a large-angle inclined fiber grating, which utilizes the mode coupling characteristic of a pair of large-angle inclined fiber gratings and the high-order mode dispersion characteristic of optical fibers to realize dispersion management, has the advantages of full optical fiber structure, large dispersion range, accurate dispersion value, low loss and the like, is beneficial to the generation of ultrashort pulse fiber laser, and promotes the practical and commercial development of the ultrafast fiber laser technology.

As shown in fig. 1 and fig. 2, the all-fiber dispersion management device based on the large-angle tilted fiber grating of the present invention includes a first large-angle tilted fiber grating, a transmission fiber, and a second large-angle tilted fiber grating, which are sequentially connected along the light transmission direction. In the invention, the transmission fiber between the first large-angle inclined fiber grating and the second large-angle inclined fiber grating can adopt common single mode fiber, small-number mode fiber or multimode fiber. Different fiber types affect the dispersion characteristics of the device, and different fiber lengths affect the magnitude of the dispersion. In practical application, according to the dispersion amount actually required by the ultra-short pulse fiber laser, the type and length of the optical fiber required by the dispersion management device are designed by calculating the high-order mode dispersion of the corresponding transmission optical fiber.

As shown in fig. 1, when the transmission fiber between two large-angle tilted fiber gratings is a single-mode fiber, the working principle is as follows: due to the mode coupling effect of the large-angle inclined fiber grating, light transmitted in the fiber core of the optical fiber is coupled to the fiber cladding of the single-mode optical fiber and transmitted when passing through the first large-angle inclined fiber grating. The light transmitted in the fiber cladding has a high-order mode, so that compared with the fundamental mode light in the fiber core in the same waveband, the dispersion characteristic is different, and smaller same dispersion characteristic, smaller or larger opposite dispersion characteristic can be realized according to the fiber characteristic and the coupled cladding mode order; after the light is transmitted for a certain distance in a high-order mode, the light is coupled from the fiber cladding to the fiber core through the second large-angle inclined fiber grating and is transmitted continuously.

As shown in fig. 2, when the transmission fiber between two large-angle tilted fiber gratings is a few-mode fiber or a multimode fiber, the working principle is as follows: due to the mode coupling effect of the large-angle inclined fiber grating, light transmitted in the fiber core of the single-mode fiber is coupled to the fiber core or the cladding of the few-mode fiber or the multimode fiber after passing through the first large-angle inclined fiber grating, and is transmitted in a high-order mode of the fiber core or the cladding. Light transmitted in a high-order mode in a few-mode fiber or a multimode fiber core or cladding has different dispersion characteristics than fundamental-mode light in a single-mode fiber core, and smaller same dispersion characteristics, smaller or larger opposite dispersion characteristics can be achieved depending on the fiber characteristics and the coupled core or cladding high-order mode order. After light continues to transmit for a certain distance in a few-mode fiber or multimode fiber core or cladding in a high-order mode, the light is coupled back to the fiber core fundamental mode from the fiber core high-order mode through the second large-angle inclined fiber grating for continuing transmission, or coupled back to the fiber core fundamental mode from the fiber cladding mode for continuing transmission.

The first large-angle inclined fiber grating and the second large-angle inclined fiber grating are different from common fiber gratings, the fiber core is provided with an inclined periodic structure, in order to realize the coupling of transmission light from the forward fiber core to the forward cladding and from the forward cladding to the forward fiber core, the inclination angle is generally larger than 66 degrees, specifically 66-89 degrees, and the specific inclination angle and the grating period are determined according to the wavelength and the bandwidth of the needed ultrashort pulse fiber laser.

When the transmission fiber between the first large-angle inclined fiber grating and the second large-angle inclined fiber grating is a single-mode fiber, the two large-angle inclined fiber gratings in the scheme can be manufactured on the same transmission fiber, or manufactured respectively and then subjected to fiber fusion. When the transmission fiber between the first large-angle inclined fiber grating and the second large-angle inclined fiber grating is a few-mode fiber or a multimode fiber, the two large-angle inclined fiber gratings in the scheme need to be manufactured and welded at two ends of a section of the few-mode fiber or the multimode fiber respectively.

The tilt directions of the first large-angle-tilt fiber grating and the second large-angle-tilt fiber grating can be the same (as in fig. 1) or opposite (as in fig. 3) along the fiber axis, and the dispersion management device can be realized. The two large-angle inclined fiber gratings can have the same parameters of inclination angle, grating period and the like, so that the two large-angle inclined fiber gratings have the same or similar coupling wavelength and bandwidth, and the maximum response bandwidth and transmission efficiency of the device are realized. The two large-angle inclined fiber gratings can also have different parameters, namely different coupling wavelengths and bandwidths, and a certain filtering effect is realized by the dislocation of the response wavelengths and the bandwidths of the two large-angle inclined fiber gratings, but the loss of devices can be increased.

In the present invention, when the dispersion of the fiber cladding mode is used, i.e. when the large-angle tilt fiber grating couples light from the fiber core to the transmission fiber cladding, if the transmission fiber has a coating layer, which is a high-folding glue, the coating layer needs to be removed or a low-folding glue needs to be coated on the fiber cladding portion of the transmission fiber, so as to prevent the light of the cladding from leaking out of the fiber and causing extra loss. If the adopted transmission optical fiber has no coating layer, the low-folding glue is directly coated without removing the coating layer.

Meanwhile, in the all-fiber dispersion management device, the adopted large-angle inclined fiber grating needs to be manufactured on the fiber with the coating removed, the large-angle inclined fiber grating can be not coated after being manufactured, or the coating needs to be selected by low-folding glue if the coating needs to be coated in order to protect the large-angle inclined fiber grating, so that the light of the cladding is prevented from leaking outside the fiber, and extra loss is caused.

In the invention, the dispersion management device is of an all-fiber structure, and the optical fibers at two ends of the device can be welded in the fiber laser cavity to provide quantitative dispersion and realize the management of net dispersion in the fiber laser cavity. The ultrashort pulse fiber laser can adopt a linear cavity or a ring cavity. In addition, the ultra-short pulse laser can also be used outside the cavity of the ultra-short fiber laser and is welded at the output fiber end of the laser to realize the compression or broadening of the ultra-short pulse laser.

Combine wide-angle slope fiber grating and optic fibre high order mode, design novel dispersion management device, compare traditional dispersion management device, novel dispersion management device based on this scheme can have a plurality of advantages such as full fiber structure, dispersion volume scope are big, dispersion value is accurate, the loss is low.

The device of the invention adopts the large-angle inclined fiber grating to realize the optical coupling of different modes in the optical fiber, so that the all-fiber dispersion management device has the following advantages: (a) compared with the traditional mode coupling modes such as stress extrusion, bending, dislocation welding and the like, the mode coupling in the optical fiber realized by the large-angle inclined fiber grating can have higher precision and coupling efficiency; (b) the large-angle inclined fiber grating is of an all-fiber structure, and has higher system integration level and reliability for the fiber laser; (c) compared with a long-period fiber grating, the large-angle inclined fiber grating has polarization response, and the polarization degree of output laser can be improved; (d) two large-angle inclined fiber gratings can be respectively designed and optimized, different coupling efficiency and response bandwidth are realized, and further parameters of devices are easier to optimize.

The device of the invention adopts the fiber high-order mode dispersion characteristic to carry out dispersion management, so that the device has the following advantages: (a) the high-order modes of different orders have different dispersion coefficients, the dispersion coefficient range of the high-order modes of the optical fiber is large, and the optical fiber is not only suitable for an ultrashort pulse laser seed source, but also suitable for systems needing pulse broadening, such as a chirped pulse amplification system; (b) the effective index of the higher-order modes of the fiber is different from the effective index of the fundamental mode and therefore has a different dispersion characteristic than the fundamental mode. When the mode order is higher than a certain value (different according to the parameters of the adopted optical fiber), the negative dispersion of the wave band below 1.3 microns can be realized, and the optical fiber has a remarkable effect on the generation of femtosecond laser with the wave band of 1 micron; (c) after the coupling mode is determined, the adjustment of the dispersion amount can be simply realized by controlling the length of the optical fiber; (d) the fiber cladding and the few-mode/multimode fiber core have large mode field area and high nonlinear threshold, and can bear higher power.