CN110673259A - A cascaded chirped long-period fiber grating bandpass filter - Google Patents

Abstract

The invention discloses a cascaded chirped long-period fiber grating band-pass filter. The filter comprises a first chirped long-period fiber grating, and a first chirped long-period fiber grating is coated on the surface of the first chirped long-period fiber grating and has a thickness greater than 2 mm. A high refractive index layer, the second chirped long period fiber grating, is coated on the surface of the second chirped long period fiber grating and has a thickness greater than 2mm. The second high refractive index layer is connected to the output end of the first chirped long period fiber grating. A cascaded single-mode fiber connected to the input end of the second chirped long-period fiber grating. The first chirped long-period fiber grating has the characteristic of band-stop filtering at a wavelength smaller than the preset center wavelength, and the second chirped long-period fiber grating has the characteristic of band-stop filtering at a wavelength greater than the preset center wavelength. After cascading single-mode fibers, a band-pass filtering effect at the preset center wavelength is formed. The invention has certain application value in the field of optical fiber communication and optical fiber sensing.

Description

A cascaded chirped long-period fiber grating bandpass filter

technical field

The invention relates to the technical fields of optical fiber communication and optical fiber sensing, in particular to a cascaded chirped long-period fiber grating bandpass filter.

Background technique

Long-period fiber grating is a transmission fiber grating with a general period greater than 10 μm. For a specific working wavelength, it can couple the energy of the core mode into the cladding mode of the same direction transmission, thereby causing the transmission loss at the corresponding wavelength. Forms the characteristics of band-stop filtering. The band-stop filtering characteristics of long-period fiber gratings are just opposite to the band-pass characteristics required in the optical fiber communication wavelength division multiplexing, so they cannot be directly used in the wavelength division multiplexing system. How to change the spectral characteristics of long-period fiber gratings and realize the effect of band-pass filtering has always been a difficult problem in the field of optical fiber communication and optical fiber sensing.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention provides a cascaded chirped long-period fiber grating band-pass filter, so as to solve the problem in the related art that it is difficult to realize the band-pass filter by using the long-period fiber grating.

For solving the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A cascaded chirped long-period fiber grating bandpass filter, comprising a first chirped long-period fiber grating, a cascaded single-mode fiber, and a second chirped long-period fiber grating, which are connected in sequence;

The surface of the first chirped long-period fiber grating is coated with a first high refractive index layer;

The surface of the second chirped long-period fiber grating is coated with a second high refractive index layer;

The thickness of the first high refractive index layer and the second high refractive index layer is greater than 2 mm;

The refractive index of the first high-refractive index layer is greater than the refractive index of the cladding layer of the first chirped long-period fiber grating;

The refractive index of the second high refractive index layer is greater than the refractive index of the cladding layer of the second chirped long-period fiber grating.

Further, the refractive index of the first high refractive index layer is 1.5-1.68, and the refractive index of the second high refractive index layer is 1.5-1.68.

Further, the first high refractive index layer and the second high refractive index layer include at least two coatings;

The materials used for the first layer of the first high-refractive index layer include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68;

The materials used for the second layer of the first high-refractive index layer include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62;

The materials used for the first layer coating of the second high refractive index layer include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68;

The materials used for the second coating of the second high refractive index layer include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62.

Further, the first chirped long-period fiber grating, the cascaded single-mode fiber, and the second chirped long-period fiber grating are connected without an eccentric core.

Further, the eccentric-free connection method includes welding.

Further, the first chirped long-period fiber grating, the cascaded single-mode fiber, and the second chirped long-period fiber grating are integrally formed.

Further, the length of the first chirped long-period fiber grating is 2cm～10cm;

The period of the first chirped long-period fiber grating is less than 150 μm;

The difference between the maximum period and the minimum period of the first chirped long-period fiber grating is 2 μm˜6 μm;

The period of the first chirped long-period fiber grating linearly increases or decreases linearly from the input end to the output end.

Further, the length of the second chirped long-period fiber grating is 2cm～10cm;

The period of the second chirped long-period fiber grating is greater than 150 μm;

The difference between the maximum period and the minimum period of the second chirped long-period fiber grating is 2 μm˜6 μm;

The period of the second chirped long-period fiber grating linearly increases or decreases linearly from the input end to the output end.

Further, the cascaded single-mode fibers include single-mode communication fibers and single-mode photosensitive fibers.

Further, the length of the cascaded single-mode fibers is 0-2 cm.

Compared with the prior art, the beneficial effects achieved by the present invention are:

In the present invention, the first high-refractive index layer and the second high-refractive index layer with a thickness of more than 2 mm are respectively coated on the surfaces of the first chirped long-period fiber grating and the second chirped long-period fiber grating, so that the cladding in the two gratings is formed. The layer mode becomes a leaky mode, so that the energy of the core layer mode in the grating can be attenuated after being coupled into the leaky mode, thus forming a good band-stop filtering effect; in addition, the first chirped long-period fiber grating and the second chirped long-period fiber grating The long-period fiber grating is cascaded by cascading single-mode fibers, so that the spectra of the two gratings overlap, and finally the band-pass filtering effect at the preset center wavelength is formed; the invention subtly changes the band-stop filtering of the long-period fiber grating It effectively solves the difficult problem of using long-period fiber grating to realize band-pass filtering.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic structural diagram of a cascaded chirped long-period fiber grating bandpass filter disclosed in an embodiment of the present invention;

FIG. 2 is a transmission spectrum diagram of a cascaded chirped long-period fiber grating bandpass filter disclosed in an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. . Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The invention discloses a cascaded chirped long-period fiber grating bandpass filter, as shown in FIG. 1 , comprising:

receiving the first chirped long-period fiber grating 100 of the input signal light;

a first high refractive index layer 101 coated on the surface of the first chirped long-period fiber grating 100 and having a thickness greater than 2 mm;

a cascaded single-mode fiber 102 connected to the first chirped long-period fiber grating 100 and receiving the signal light output by the first chirped long-period fiber grating 100;

a second chirped long-period fiber grating 103 connected to the cascaded single-mode fiber 102, receiving the signal light output by the cascaded single-mode fiber 102 and outputting it;

A second high refractive index layer 104 with a thickness greater than 2 mm is coated on the surface of the second chirped long-period fiber grating 103 .

The first chirped long-period fiber grating 100 and the second chirped long-period fiber grating 103 may also be referred to as the first-stage chirped long-period fiber grating and the second-stage chirped long-period fiber grating, respectively.

The first chirped long-period fiber grating 100, the cascaded single-mode fiber 102, and the second chirped long-period fiber grating 103 are the same single-mode fiber, and the first chirped long-period fiber grating 100 and the second chirped long-period fiber The grating 103 is written on this single-mode fiber, and the single-mode fiber between the first chirped long-period fiber grating 100 and the second chirped long-period fiber grating 103 is the cascaded single-mode fiber 102 .

The first chirped long-period fiber grating 100 and the second chirped long-period fiber grating 103 can also be written on different single-mode fibers respectively, and then connected by cascading single-mode fibers 102 without polarization cores. Methods include fusion splicing, or other methods that can connect three lengths of fiber.

The first chirped long-period fiber grating 100 includes: a chirped long-period fiber grating written by an ultraviolet exposure method and a chirped long-period fiber grating written by a CO ₂ laser.

The first high refractive index layer 101 at least completely covers the first chirped long-period fiber grating 100 segments.

The second chirped long-period fiber grating 103 includes a chirped long-period fiber grating written by an ultraviolet exposure method and a chirped long-period fiber grating written by a CO ₂ laser.

The second high refractive index layer 104 at least completely covers the second chirped long-period fiber grating 103 segment.

The length of the first chirped long-period fiber grating 100 is 2 cm to 10 cm, the period of the first chirped long-period fiber grating 100 is less than 150 μm, and linearly increases or decreases linearly from the input end to the output end, and the maximum and minimum period are The difference is 2μm~6μm.

The refractive index of the first high refractive index layer 101 is greater than the refractive index of the cladding layer of the first chirped long-period fiber grating 100 .

The length of the second chirped long-period fiber grating 103 is 2cm~10cm, the period of the second chirped long-period fiber grating 103 is greater than 150 μm, and linearly increases or decreases linearly from the input end to the output end. The difference is 2 μm to 6 μm.

In the present invention, by setting the period range, the first chirped long-period fiber grating 100 exhibits band-stop filtering characteristics when the wavelength is less than the preset center wavelength, while the second chirped long-period fiber grating 103 exhibits the characteristics of band-stop filtering when the wavelength is greater than the preset center wavelength. characteristics of band-stop filtering.

The refractive index of the second high refractive index layer 104 is greater than the refractive index of the cladding layer of the second chirped long-period fiber grating 103 .

The refractive index of the first high refractive index layer 101 is 1.5˜1.68, and the refractive index of the second high refractive index layer 104 is 1.5˜1.68.

The materials used for the first high refractive index layer 101 and the second high refractive index layer 104 may be polysulfone resin, parylene, polyvinyl chloride, and polyacrylate.

The first high refractive index layer 101 and the second high refractive index layer 104 include at least two layers of coating;

The materials used for the first coating of the first high refractive index layer 101 include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68;

The materials used for the second coating layer of the first high refractive index layer 101 include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62;

The materials used for the first coating layer of the second high refractive index layer 104 include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68;

The materials used for the second coating of the second high refractive index layer 104 include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62.

A specific embodiment of the present invention is given below.

The first chirped long-period fiber grating 100 and the second chirped long-period fiber grating 103 are written on the same single-mode fiber, and the parameters of the single-mode fiber are: the core diameter is 5 μm, the core refraction The ratio is 1.458, the cladding diameter is 125 μm, and the cladding refractive index is 1.45. The single-mode fiber parameters here are preferably set, but are not limited to the fixed values.

The length of the first chirped long-period fiber grating 100 is 6 cm, the grating period increases linearly from 85 μm to 88 μm, and the refractive index modulation depth is 8×10 ⁻⁴ . The first high-refractive index layer coated on the surface of the first long-period fiber grating 100 includes two layers of coatings, wherein the refractive index of the first coating is 1.65 and the thickness is 1.5 mm, and the coating is directly coated on the first coating. The surface of the chirped long-period fiber grating 100; the second coating has a refractive index of 1.55 and a thickness of 1.5 mm, and is coated on the surface of the first coating. Here, the parameters of the first chirped long-period fiber grating 100 and the parameters of the first high-refractive index layer 101 are preferably set, but are not limited to the fixed values.

The length of the second long-period fiber grating 103 is 3 cm, the grating period increases linearly from 220 μm to 224 μm, and the refractive index modulation depth is 8×10 ⁻⁴ . The second high refractive index layer coated on the surface of the second chirped long-period fiber grating 103 includes two layers of coatings, wherein the first coating has a refractive index of 1.65 and a thickness of 1.8 mm, and the coating is directly coated on the surface. The surface of the second chirped long-period fiber grating; the second coating has a refractive index of 1.58 and a thickness of 1.2 mm, and is coated on the surface of the first coating. Here, the parameters of the second chirped long-period fiber grating 103 and the parameters of the second high refractive index layer 104 are preferably set, but are not limited to the fixed values.

The single-mode fiber between the first chirped long-period fiber grating 100 and the second chirped long-period fiber grating 103 is the cascaded single-mode fiber 102, and the length of the cascaded single-mode fiber 102 is 1 cm. Here, the length of the cascaded single-mode fibers 102 is a preferred setting, but is not limited to the fixed value.

The realization principle of the cascaded chirped long-period fiber grating bandpass filter is as follows:

The surfaces of the first chirped long-period fiber grating and the second chirped long-period fiber grating are coated with a high refractive index layer with a thickness of more than 2 mm, so the cladding modes in the two gratings are leaky modes. The period range of the first chirped long-period fiber grating can make the core mode and the leaky mode in the first chirped long-period fiber grating satisfy the phase matching condition at a short wavelength less than the preset center wavelength, so, at a wavelength less than the preset center wavelength, Assuming that at the short wavelength of the center wavelength, the core mode energy in the first chirped fiber grating will be coupled into the leakage mode and lost, thereby forming the characteristics of short-wavelength band-stop filtering; the second chirped long-period fiber grating has the characteristics of The period range can make the core mode and the leakage mode in the second chirped long-period fiber grating satisfy the phase matching condition at the long wavelength greater than the preset center wavelength. Therefore, at the long wavelength greater than the preset center wavelength, the second chirped The core mode energy in the long-period fiber grating will be coupled into the leaky mode and lost, forming the characteristics of long-wavelength band-stop filtering; the first chirped long-period fiber grating and the second chirped long-period fiber grating pass through the cascaded single After the mode fibers are cascaded, the spectra of the two gratings overlap, finally forming a band-pass filtering effect at the preset center wavelength.

FIG. 2 is a transmission spectrum diagram of a cascaded chirped long-period fiber grating bandpass filter in a separate embodiment of the present invention. It can be seen from the spectrogram that the filter is a band-pass filter with a center wavelength of 1.5 μm and a 3dB bandwidth of 130 nm.

It should be noted that, the cascaded chirped long-period fiber grating bandpass filter disclosed in this embodiment only needs to write two periods of a specific length on a single-mode fiber to linearly change within their respective preferred setting ranges. The chirped long-period fiber grating of the chirped long-period fiber grating is then simply physically coated on the surfaces of the two chirped long-period fiber gratings. The fabrication is simple, the stability is good, and the mass production is easy.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments may be referred to each other.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. a cascaded chirped long-period fiber grating bandpass filter, it is characterized in that, comprise the first chirped long-period fiber grating, cascaded single-mode fiber and the second chirped long-period fiber grating that are successively connected and set; The surface of the first chirped long-period fiber grating is coated with a first high refractive index layer; The surface of the second chirped long-period fiber grating is coated with a second high refractive index layer; The thickness of the first high refractive index layer and the second high refractive index layer is greater than 2 mm; The refractive index of the first high-refractive index layer is greater than the refractive index of the cladding layer of the first chirped long-period fiber grating; The refractive index of the second high refractive index layer is greater than the refractive index of the cladding layer of the second chirped long-period fiber grating. 2 . The cascaded chirped long-period fiber grating bandpass filter according to claim 1 , wherein the refractive index of the first high refractive index layer is 1.5˜1.68, and the second high refractive index layer has a refractive index of 1.5 to 1.68. 3 . The refractive index is 1.5~1.68. 3. A cascaded chirped long-period fiber grating bandpass filter according to claim 2, wherein the first high-refractive index layer and the second high-refractive index layer comprise at least two coatings; The materials used for the first layer of the first high-refractive index layer include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68; The materials used for the second layer of the first high-refractive index layer include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62; The materials used for the first layer coating of the second high refractive index layer include polysulfone resin and parylene, the thickness is greater than 1 mm, and the refractive index is 1.62-1.68; The materials used for the second coating of the second high refractive index layer include polyvinyl chloride and polyacrylate, the thickness is greater than 1 mm, and the refractive index is 1.5-1.62. 4. A cascaded chirped long-period fiber grating bandpass filter according to claim 1, wherein the first chirped long-period fiber grating, the cascaded single-mode fiber and the second chirped long-period fiber There is no eccentric connection between periodic fiber gratings. 5 . The cascaded chirped long-period fiber grating bandpass filter according to claim 4 , wherein the non-eccentric connection method comprises fusion splicing. 6 . 6. A cascaded chirped long-period fiber grating bandpass filter according to claim 1, wherein the first chirped long-period fiber grating, the cascaded single-mode fiber and the second chirped long-period fiber The periodic fiber grating is an integral molding structure. 7. a kind of cascaded chirped long-period fiber grating bandpass filter according to claim 1, is characterized in that, the length of described first chirped long-period fiber grating is 2cm～10cm; The period of the first chirped long-period fiber grating is less than 150 μm; The difference between the maximum period and the minimum period of the first chirped long-period fiber grating is 2 μm˜6 μm; The period of the first chirped long-period fiber grating linearly increases or decreases linearly from the input end to the output end. 8. The cascaded chirped long-period fiber grating bandpass filter according to claim 1, wherein the length of the second chirped long-period fiber grating is 2cm～10cm; The period of the second chirped long-period fiber grating is greater than 150 μm; The difference between the maximum period and the minimum period of the second chirped long-period fiber grating is 2 μm˜6 μm; The period of the second chirped long-period fiber grating linearly increases or decreases linearly from the input end to the output end. 9 . The cascaded chirped long-period fiber grating bandpass filter according to claim 1 , wherein the cascaded single-mode fibers comprise single-mode communication fibers and single-mode photosensitive fibers. 10 . 10 . The cascaded chirped long-period fiber grating bandpass filter according to claim 1 , wherein the length of the cascaded single-mode fibers is 0˜2 cm. 11 .

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