CN103941330A - Composite structure long-period fiber grating - Google Patents

Abstract

The invention discloses a composite structure long-period fiber grating which comprises a fiber core, a fiber cladding and a fiber coating, wherein the fiber cladding coats the outside of the fiber core, the fiber coating coats the outside of the fiber cladding, and the fiber core belongs to the long-period fiber grating formed by a vertically staggered composite structure. The composite structure long-period fiber grating has a fine environmental response characteristic and a fine polarization characteristic, refractivity is vertically distributed in a staggered manner, and a fiber grating structure is enriched.

Description

A Composite Structure Long Period Fiber Bragg Grating

technical field

The invention relates to an optical fiber grating, in particular to a compound structure long-period optical fiber grating.

Background technique

Fiber Bragg Grating has the advantages of simple manufacturing process, low insertion loss, full compatibility with optical fibers, small size, and can be embedded in smart materials. It has been widely used in the fields of optical fiber communication and optical fiber sensing. Long-period fiber grating refers to a fiber grating with a grating period greater than 1 micron. Its coupling feature is the energy exchange between the fundamental mode transmitted in the core and the cladding modes of different orders transmitted in the cladding, resulting in a The related transmission loss is a very good band-stop filter device, and has the advantages of small additional loss, small back reflection, small size, etc., and can be widely used in optical fiber communication and sensing.

Since the advent of long-period fiber gratings in 1996, a variety of grating processing technologies have been proposed. Among them, the laser writing technology represented by ultraviolet exposure method and carbon dioxide laser technology has been vigorously developed. In recent years, with the development of the Internet of Things, long-period fiber gratings and core sensor devices have been vigorously developed. The basic sensing principle of long-period fiber gratings as optical fiber sensors is: when external environmental parameters such as temperature, strain, pressure, When the refractive index of the environment changes, the parameters of the resonant wavelength of the grating (generally referred to as the harmonic peak) such as wavelength position, amplitude, and polarization state change, so as to detect the change of the external environmental parameter by measuring the change of the harmonic wavelength parameter size, which realizes the measurement of environmental parameters. On the other hand, the period of the long-period fiber grating is relatively long, and the phase-matching condition is satisfied by the core fundamental mode and cladding mode propagating in the same direction, which will lead to long-period fiber The parameters of the resonant wavelength of the grating are very sensitive to changes in the external environment, so it has good sensitivity to temperature, strain, bending, twist, lateral load, concentration and refractive index. With the development of integration and miniaturization of optical fiber devices, There is an urgent need for long-period fiber gratings with multiple functions and multi-performance. Although there are different methods for writing long-period fiber gratings, the grating distribution (that is, the distribution of refractive index along the cross-section of the fiber core) has a single structure, which affects the long-period fiber grating. Development of periodic fiber gratings.

At present, there are mainly two forms of long-period fiber grating structures in the world according to the distribution of the refractive index of the cross-section of the grating. One is a uniform long-period fiber grating, that is, the refractive index changes uniformly along the cross-section of the optical fiber. The environmental response characteristics, that is, the sensing characteristics, but because the refractive index is uniformly distributed along the cross-section of the fiber and has no polarization-related characteristics, it is not suitable for some special purposes, such as long-wavelength fiber lasers, etc.; the other is tilted long-period fiber gratings, Since the refractive index distribution of the grating is non-uniform along the cross-section of the optical fiber, it has good polarization-dependent characteristics; however, due to the uneven distribution of the refractive index of the tilted grating and the need to accurately control the tilt angle, the difficulty of making the grating increases. Not easy to mass produce.

Contents of the invention

In order to overcome the defects of the prior art, the invention provides a long-period optical fiber grating with composite structure that is simple to manufacture and rich in structural changes.

The invention discloses a composite structure long-period fiber grating, comprising a fiber core, an optical fiber cladding covering the outside of the fiber core and an optical fiber coating covering the outside of the fiber cladding, the fiber core is The core of the long-period fiber grating formed by the upper and lower dislocation composite structure.

The long-period fiber grating of the fiber core has a uniform period or a non-uniform period.

Compared with the prior art, a composite structure long-period fiber grating of the present invention has the following advantages:

1) Good environmental response characteristics, because the refractive index of the grating is asymmetrically distributed on the cross-section of the grid, it is beneficial to the environmental response characteristics, that is, the sensing characteristics;

2) Good polarization-dependent characteristics, the refractive index is staggered up and down along the fiber core, which is conducive to the response of polarization-dependent characteristics;

3) The structure of the fiber grating is enriched. At present, the grating refractive index distribution of the fiber grating is relatively single, but the grating structure of the composite structure in the present invention is conducive to the development of the grating structure to a multi-form grating structure, enriches the structure of the grating, and expands Applications of fiber gratings.

Description of drawings

Figure 1a is a schematic structural view of a composite structure long-period fiber grating of the present invention;

Fig. 1b is a cross-sectional refractive index distribution diagram of a composite structure long-period fiber grating of the present invention;

Figure 2a is a schematic structural view of an existing uniform long-period fiber grating;

Figure 2b is a cross-sectional refractive index distribution diagram of an existing uniform long-period fiber grating;

Figure 3a is a schematic structural view of an existing tilted long-period fiber grating;

Fig. 3b is a cross-sectional refractive index distribution diagram of an existing tilted long-period fiber grating.

Detailed ways

The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

As shown in Figure 1a, a composite structure long period fiber grating disclosed by the present invention includes a core 1, an optical fiber cladding 2 coated outside the core and an optical fiber clad outside the optical fiber cladding. The coating layer 3, the fiber core 1 is the fiber core of the long period fiber grating formed by the up-and-down dislocation composite structure, the grating is uniform period or non-uniform period, and the size of the formed light spot can also be adjusted.

As shown in Figure 1b, in the long-period fiber grating with composite structure disclosed by the present invention, the refractive index of the grating presents a semicircular distribution on the cross-section of the grating, that is, half of the core refractive index changes on the cross-section of the core. The other half remains unchanged, and the refractive index is asymmetrically distributed in the cross section, which is beneficial to the response of polarization-dependent characteristics; at the same time, the grating periodic refractive index is distributed up and down along the fiber core, and this structure is conducive to the environment of the grating. Response characteristics, that is, sensing characteristics.

As shown in Figure 2a, the core in the uniform long-period fiber grating is the core 4 of the uniformly distributed grating, and its grating refractive index is uniformly distributed along the cross-section of the fiber core as shown in Figure 2b. When the core and cladding are coupled, the transmission spectrum has no polarization-dependent properties due to the uniform distribution of the core refractive index.

As shown in Figure 3a, the core in the tilted long-period fiber grating is the core 5 of the uniformly tilted distribution grating, and the refractive index of the grating is distributed along the inclined distribution of the fiber core as shown in Figure 2b. The distribution is uneven, so it has good polarization characteristics, but because the refractive index of the tilted grating is distributed along the fiber core, it is difficult to manufacture, and it is difficult to precisely control the tilt angle of the grating.

In addition, a long-period fiber grating with a composite structure disclosed by the present invention not only has good environmental response characteristics, but also has good polarization-related characteristics, and can be used as a filter with good performance in the fields of optical communication and optical sensing. At the same time, its refractive index presents an up and down staggered distribution, which enriches the fiber grating structure. By designing the distribution of the refractive index of the composite long-period fiber grating at different positions in the fiber core, it can be made into a grating structure with different spectral characteristics, which broadens the fiber grating Applications.

The technical contents and technical features of the present invention have been disclosed above, but those skilled in the art may still make various replacements and modifications based on the disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the embodiments The disclosed content should include various replacements and modifications that do not depart from the present invention, and are covered by the claims of this patent application.

Claims (2)

1. a composite structure long period fiber grating, comprise fibre core, be coated on the fibre cladding of described fibre core outside and be coated on the optical fiber coating of described fibre cladding outside, it is characterized in that: described fibre core is the fibre core of the long period fiber grating that composite structure forms of misplacing up and down.

2. a kind of composite structure long period fiber grating according to claim 1, is characterized in that: the long period fiber grating of described fibre core is uniform period or non-homogeneous cycle.