阅读说明：本技术 一种纤维集成的可调光梳状滤波器、方法和光系统 (Fiber-integrated adjustable optical comb filter, method and optical system ) 是由 郑狄 罗成明 邹喜华 罗斌 于 2021-08-04 设计创作，主要内容包括：本发明公开了一种纤维集成的可调光梳状滤波器、方法和光系统,滤波器包括具有锥形耦合器的双芯光纤,所述双芯光纤包括对称分布在光纤中性轴两侧的第一纤芯和第二纤芯；在第一纤芯和第二纤芯上相对于锥形耦合器的同一侧,分别刻写有两个参数一致的非倾斜的光纤光栅,两个光纤光栅沿光纤长度方向上的不同位置处；所述锥形耦合器为3dB耦合器。本发明将传统方案中所需分立器件均在一段双芯光纤集成实现,锥形耦合器通过对双芯光纤熔融拉锥实现,而Michelson干涉仪的两臂结构通过在两个纤芯中分别写入的光纤光栅实现,集成度高、稳定性好并且实现了器件的小型化。(The invention discloses a fiber-integrated adjustable optical comb filter, a method and an optical system, wherein the filter comprises a dual-core optical fiber with a tapered coupler, and the dual-core optical fiber comprises a first fiber core and a second fiber core which are symmetrically distributed on two sides of a neutral axis of the optical fiber; respectively writing two non-inclined fiber gratings with the same parameters on the first fiber core and the second fiber core at the same side relative to the conical coupler, wherein the two fiber gratings are at different positions along the length direction of the optical fiber; the tapered coupler is a 3dB coupler. According to the invention, all discrete devices required in the traditional scheme are integrated in a section of double-core optical fiber, the tapered coupler is realized by melting and tapering the double-core optical fiber, and the two-arm structure of the Michelson interferometer is realized by respectively writing optical fiber gratings in the two fiber cores, so that the integration level is high, the stability is good, and the miniaturization of the devices is realized.)

1. A fiber-integrated tunable optical comb filter, comprising: the dual-core optical fiber comprises a dual-core optical fiber with a conical coupler, wherein the dual-core optical fiber comprises a first fiber core and a second fiber core which are symmetrically distributed on two sides of a neutral axis of the optical fiber; respectively writing two non-inclined fiber gratings with the same parameters on the first fiber core and the second fiber core at the same side relative to the conical coupler, wherein the two fiber gratings are at different positions along the length direction of the optical fiber; the tapered coupler is a 3dB coupler.

2. A fiber-integrated tunable optical comb filter according to claim 1, wherein: the fiber grating is a uniform fiber Bragg grating or a linear chirped fiber grating.

3. A fiber-integrated tunable optical comb filter according to claim 1, wherein: when the double-core optical fiber 1 is not bent, the position interval of the two optical fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when the comb-shaped fiber is bent along the plane direction of the two fiber cores, the center wavelength of each channel of the comb-shaped spectrum can be tuned.

4. A fiber-integrated tunable optical comb filter according to claim 1, wherein: the non-tapered coupler portions of the fiber cores are all parallel to each other, and the grating plane is consistent with the plane formed by the first fiber core and the second fiber core.

5. A method for using a fiber-integrated tunable optical comb filter according to any one of claims 1 to 4, wherein: the method comprises the following steps:

an optical signal input from the first fiber core passes through a tapered coupler and then outputs two paths of signals from an A1 port and an A2 port respectively, the A1 port is one end of the tapered coupler close to the side of the fiber grating, the A2 port is the other end of the tapered coupler close to the side of the fiber grating, the A1 port is located on the first fiber core, and the A2 port is located on the second fiber core;

when two paths of optical signals respectively pass through the first fiber bragg grating and the second fiber bragg grating, the optical signals are reflected back, and interference is generated at the conical coupler after the optical signals return through the original path;

an interference signal is output from the first core.

6. An optical system, characterized by: the method comprises the following steps:

a fiber-integrated tunable optical comb filter according to any one of claims 1 to 4;

the single-mode fiber is arranged on one side, away from the fiber grating, of the tapered coupler and is connected with the first fiber core;

and the reflection port of the optical circulator is connected with the single-mode optical fiber.

7. A preparation method of a fiber-integrated tunable optical comb filter is characterized by comprising the following steps: the method comprises the following steps:

constructing a tapered coupler on a double-core optical fiber in a fused biconical taper mode, wherein the double-core optical fiber comprises a first fiber core and a second fiber core which are symmetrically distributed on two sides of a neutral axis of the optical fiber, and the tapered coupler is a 3dB coupler;

and respectively writing non-inclined fiber gratings with consistent parameters on the same side of the first fiber core and the second fiber core relative to the tapered coupler, wherein the two fiber gratings are at different positions along the length direction of the optical fiber.

8. The method of claim 7, wherein the method comprises: the fiber grating is a uniform fiber Bragg grating or a linear chirped fiber grating.

9. The method of claim 7, wherein the method comprises: when the double-core optical fiber is not bent, the position interval of the two optical fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when the comb-shaped fiber is bent along the plane direction of the two fiber cores, the center wavelength of each channel of the comb-shaped spectrum can be tuned.

10. The method of claim 7, wherein the method comprises: the non-tapered coupler portions of the fiber cores are all parallel to each other, and the grating plane is consistent with the plane formed by the first fiber core and the second fiber core.

Technical Field

The invention relates to the field of optical fibers, in particular to a fiber-integrated adjustable optical comb filter, a method and an optical system.

Background

Currently, the transmission capacity of a single-core optical fiber is close to its physical limit, and in order to meet the capacity requirement of a future communication system, a multi-core optical fiber attracts people's attention. On the other hand, the development and progress of multi-core fiber technology also introduces new energy into the fusion of integrated optics and fiber optics. By means of multi-waveguide structures in different optical fibers, various optical paths and optical devices are integrated into one optical fiber in a micro mode through multi-path light splitting and light combining in a single optical fiber, and the integration of the optical paths and the optical devices into one optical fiber is achieved, for example, the optical devices such as a Mach-Zehnder interferometer, a multi-mode interferometer and an optical modulator are integrated into a single optical fiber.

In 2006, researchers at Harbin engineering university have proposed symmetric dual-core fiber-based Michelson interferometer curvature sensors (Yuan L B, Yang J, Liu Z H, et al. in-fiber integrated Michelson interferometer [ J ]. Optics Letters,2006,31(18): 2692-. The sensor is tapered at the welding point of the single-mode optical fiber and the double-core optical fiber, and a reflective film is arranged at the tail end of the double-core optical fiber, so that a far-field interference pattern is generated. Curvature demodulation is achieved by analyzing the phase shift amount of the far-field interferogram. In 2016, researchers at the university of China proposed a heterogeneous seven-core fiber-based Michelson interferometer temperature sensor (Duan L, Zhang P. Tang M, et al. heterogeneously all-supported multi fiber based multi channel interferometer for high temperature sensing [ J ]. Optics Express,2016,24(8): 20210-20218). The sensor is a Michelson interferometer structure which realizes multipath interference by tapering at the welding point of the single-mode optical fiber and the seven-core optical fiber and forming a spherical reflection structure by arc discharge at the other end face of the seven-core optical fiber.

The existing Michelson interferometer based on the multi-core fiber is used in the sensing field, and the demodulation of the parameter to be measured is realized by analyzing the change of the interference spectrum. The interference spectrum of the existing multi-core fiber Michelson interferometer is periodic in the whole spectrum range, the free spectrum range is usually dozens of nanometers, and comb spectrum can not be realized in a certain specific passband, so that the multi-core fiber Michelson interferometer is difficult to be used in the communication field.

The double-core optical fiber has the characteristics of integration of fibers for realizing functional devices, small volume, convenience for integration with other functional devices and high stability, but the double-core optical fiber does not have a precedent for realizing the whole fiber integrated adjustable optical comb filter.

Therefore, in the prior art, a fiber-integrated tunable optical comb filter, a method and an optical system manufactured by using a dual-core optical fiber structure belong to the problems to be solved in the field.

Disclosure of Invention

The present invention is directed to overcome the deficiencies of the prior art and to provide a fiber-integrated tunable optical comb filter, a method and an optical system.

The purpose of the invention is realized by the following technical scheme:

in a first aspect of the present invention, a fiber-integrated tunable optical comb filter is provided, which includes a dual-core optical fiber having a tapered coupler, where the dual-core optical fiber includes a first fiber core and a second fiber core symmetrically distributed on two sides of a neutral axis of the optical fiber; respectively writing two non-inclined fiber gratings with the same parameters on the first fiber core and the second fiber core at the same side relative to the conical coupler, wherein the two fiber gratings are at different positions along the length direction of the optical fiber; the tapered coupler is a 3dB coupler.

Further, the fiber grating is a uniform Bragg fiber grating or a linear chirped fiber grating.

Further, when the double-core optical fiber is not bent, the position interval of the two fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when the comb-shaped fiber is bent along the plane direction of the two fiber cores, the center wavelength of each channel of the comb-shaped spectrum can be tuned.

Furthermore, the non-tapered coupler parts of the fiber cores are all parallel to each other, and the grating plane is consistent with the plane formed by the first fiber core and the second fiber core.

In a second aspect of the present invention, a method for using the fiber-integrated tunable optical comb filter is provided, which includes the following steps:

an optical signal input from the first fiber core passes through a tapered coupler and then outputs two paths of signals from an A1 port and an A2 port respectively, the A1 port is one end of the tapered coupler close to the side of the fiber grating, the A2 port is the other end of the tapered coupler close to the side of the fiber grating, the A1 port is located on the first fiber core, and the A2 port is located on the second fiber core;

when two paths of optical signals respectively pass through the first fiber bragg grating and the second fiber bragg grating, the optical signals are reflected back, and interference is generated at the conical coupler after the optical signals return through the original path;

output from the first core.

In a third aspect of the invention, there is provided an optical system comprising:

the fiber-integrated tunable optical comb filter;

the single-mode fiber is arranged on one side, away from the fiber grating, of the tapered coupler and is connected with the first fiber core;

and the reflection port of the optical circulator is connected with the single-mode optical fiber.

The fourth aspect of the present invention provides a method for preparing a fiber-integrated tunable optical comb filter, which comprises the following steps:

constructing a tapered coupler on a double-core optical fiber in a fused biconical taper mode, wherein the double-core optical fiber comprises a first fiber core and a second fiber core which are symmetrically distributed on two sides of a neutral axis of the optical fiber, and the tapered coupler is a 3dB coupler;

and respectively writing non-inclined fiber gratings with consistent parameters on the same side of the first fiber core and the second fiber core relative to the tapered coupler, wherein the two fiber gratings are at different positions along the length direction of the optical fiber.

Further, the fiber grating is a uniform Bragg fiber grating or a linear chirped fiber grating.

Further, when the double-core optical fiber is not bent, the position interval of the two fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when the comb-shaped fiber is bent along the plane direction of the two fiber cores, the center wavelength of each channel of the comb-shaped spectrum can be tuned.

Furthermore, the non-tapered coupler parts of the fiber cores are all parallel to each other, and the grating plane is consistent with the plane formed by the first fiber core and the second fiber core.

In a fifth aspect of the present invention, a device for manufacturing a fiber-integrated tunable optical comb filter is provided, which has the same inventive concept as the manufacturing method, and includes:

the fusion splicer is used for constructing a tapered coupler on the double-core optical fiber in a fused biconical taper mode, the double-core optical fiber comprises a first fiber core and a second fiber core which are symmetrically distributed on two sides of a neutral axis of the optical fiber, and the tapered coupler is a 3dB coupler;

and the writing device is used for respectively writing non-inclined fiber gratings with consistent parameters on the same side of the first fiber core and the second fiber core relative to the tapered coupler, and the two fiber gratings are arranged at different positions along the length direction of the optical fiber.

Further, the fiber grating is a uniform Bragg fiber grating or a linear chirped fiber grating.

Further, when the double-core optical fiber is not bent, the position interval of the two fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when the comb-shaped fiber is bent along the plane direction of the two fiber cores, the center wavelength of each channel of the comb-shaped spectrum can be tuned.

Furthermore, the non-tapered coupler parts of the fiber cores are all parallel to each other, and the grating plane is consistent with the plane formed by the first fiber core and the second fiber core.

The invention has the beneficial effects that:

in an exemplary embodiment of the invention, discrete devices (such as a 3dB coupler, an SMF for constructing two arms of a Michelson interferometer) required in a conventional scheme are integrated and implemented in a section of dual-core fiber, so that the integration is high, the stability is good, and the miniaturization of the device is realized. That is to say, only a single two-core optical fiber is needed to realize the scheme of the fiber-integrated tunable optical comb filter: the conical coupler is realized by tapering the double-core optical fiber; and the two-reflection signal channel structure of the Michelson interferometer is realized by writing non-inclined fiber gratings in the two fiber cores respectively.

In addition, because the two fiber gratings are arranged at different positions along the length direction of the optical fiber, the reflection spectrums of the two uniform fiber Bragg gratings or the linear chirped fiber gratings with the same parameters determine the wavelength position of the comb spectrum passband and the comb spectrum envelope bandwidth of the fiber integrated adjustable optical comb filter. When the double-core optical fiber is not bent, the position interval of the two fiber gratings in the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum. When bending along the plane of the two cores, one core is in tensile strain and the other core is in compressive strain because the two cores are located on either side of the neutral axis of the fiber. The bending causes the length and the refractive index of the two fiber cores to be no longer the same, so that the phase shift amount of the reflected signals of the two fiber cores is no longer the same, and the central wavelength of each channel of the output comb spectrum can be tuned.

The corresponding method of use, light system, method of preparation and preparation device also have the same advantages.

Drawings

FIG. 1 is a schematic diagram of a Michelson interferometer of the prior art;

FIG. 2 is a schematic diagram of a fiber-integrated tunable optical comb filter according to an exemplary embodiment of the present invention;

FIG. 3 is a schematic diagram of a light system architecture in a further exemplary embodiment of the invention;

FIG. 4 is a flow chart of a method for making a fiber-integrated tunable optical comb filter in an exemplary embodiment of the invention;

in the figure, 1-double-core fiber, 2-conical coupler, 3-fiber core, 301-first fiber core, 302-second fiber core, 4-fiber grating, 401-first fiber grating, 402-second fiber grating, 5-single-mode fiber and 6-optical circulator.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that directions or positional relationships indicated by "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like are directions or positional relationships described based on the drawings, and are only for convenience of description and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

It is to be understood that although the terms first, second, third, etc. may be used herein to describe various information, such information should not be limited to these terms. These terms are only used to distinguish different types of information from each other. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the present application. The word "if" as used herein may be interpreted as "at … …" or "when … …" or "in response to a determination", depending on the context. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The principle of the Michelson interferometer is that one incident beam is divided into two beams by a beam splitter and then the two beams are reflected by corresponding plane mirrors respectively, and the two beams have the same optical frequency, the same vibration direction and constant phase difference (namely, the interference condition is met), so that interference can occur. The different optical paths of the two beams in interference can be realized by adjusting the length of the interference arm and changing the refractive index of the medium, so that different interference patterns can be formed, namely the dressing filter.

The double-core optical fiber is a special optical fiber with special refractive index distribution, breaks through the refractive index distribution structure of the conventional optical fiber, and two parallel fiber cores are arranged in a single optical fiber, so that the double-core optical fiber can be used as an optical transmission medium and can construct a new optical device. Compared with a single-mode optical fiber, the double-core optical fiber has the characteristics of integration of fibers for realizing functional devices, small volume, convenience for integration with other functional devices and high stability, but the double-core optical fiber is not precedent for realizing the Michelson total reflection mirror.

Accordingly, in the following exemplary embodiments, the problems to be solved in the art are solved, and a fiber-integrated tunable optical comb filter, a method and an optical system fabricated in a structure of a dual-core optical fiber are provided.

Referring to fig. 2, fig. 2 shows a fiber-integrated tunable optical comb filter provided by an exemplary embodiment of the present invention, which includes a dual-core optical fiber 1 having a tapered coupler 2, where the dual-core optical fiber 1 includes a first core 301 and a second core 302 symmetrically distributed on two sides of a neutral axis of the optical fiber; non-inclined fiber gratings 4 with consistent parameters are written on the same side of the first fiber core 301 and the second fiber core 302 relative to the tapered coupler 2, and the two fiber gratings 4 are arranged at different positions along the length direction of the optical fiber; the tapered coupler 2 is a 3dB coupler.

It should be noted that the dual-core optical fiber 1 has two fiber cores 3 in the cladding, and belongs to a special optical fiber; from the physical structure of the optical waveguide, the dual-core optical fiber 1 is mainly classified into a coaxial dual-core optical fiber and a non-coaxial dual-core optical fiber. The coaxial dual-core fiber is also called a double-clad fiber or a double-core fiber, that is, two fiber cores 3 in the cladding are on the same axis with the center of the cladding as the axis, and represent the structure of the inner and outer fiber cores 3. While the present exemplary embodiment employs a non-coaxial type of two-core fiber 1, the non-coaxial two-core fiber 1 is a fiber in which two independent cores 3 are present in a cladding.

In addition, the non-coaxial dual-core fiber can be divided into a non-coaxial dual-core fiber that is axisymmetric (with respect to the center of the fiber cladding) and a non-coaxial dual-core fiber that is offset from the axis. The two cores 3 of the non-coaxial twin core fiber with the axis offset are still parallel cores, but the symmetry axes of the two cores 3 are offset to the fiber side. Typically, for example, one of the cores 3 may be located exactly on the central axis of the entire dual-core fiber 1. In the present exemplary embodiment and in the figures, however, axisymmetric non-coaxial symmetric dual-core fibers are used, i.e., the two cores 3 are symmetric to the neutral axis of the fiber.

Specifically, when the fiber-integrated tunable optical comb filter in the present exemplary embodiment is used, two paths of signals are output from an a1 port and an a2 port respectively after an optical signal input from the first fiber core 301 passes through the tapered coupler 2 (when A3 dB coupler is used as the tapered coupler, the optical signal is uniformly distributed to the two fiber cores 3 after passing through the 3dB coupler), the a1 port is one end of the tapered coupler 301 close to the fiber grating 4 side, the a2 port is the other end of the tapered coupler 2 close to the fiber grating 4 side, the a1 port is located on the first fiber core 301, and the a2 port is located on the second fiber core 302;

when two optical signals respectively pass through the first fiber bragg grating 401 and the second fiber bragg grating 402, the optical signals are reflected back due to the same fiber bragg gratings 4 in the two fiber cores 3, and interference is generated at the conical coupler 2 after the optical signals return through the original path;

at this point, an interference signal will be output from the first core 301.

Therefore, when the fiber-integrated tunable optical comb filter constructed by the dual-core optical fiber 1 according to the present exemplary embodiment is adopted, discrete devices (such as a 3dB coupler and SMFs constructing two arms of a Michelson interferometer) required in the conventional scheme are integrated and implemented in one segment of the dual-core optical fiber 1, so that the integration is high, the stability is good, and the miniaturization of the device is realized. That is, only a single dual-core optical fiber 1 is needed to realize a scheme of the fiber-integrated tunable optical comb filter: the conical coupler 2 is realized by tapering the double-core optical fiber 1; and the Michelson interferometer type structure is realized by a 3dB coupler and non-inclined fiber gratings 4 respectively written in the two cores 3.

It should be noted that, in a preferred exemplary embodiment, in addition, since the two fiber gratings 4 are at different positions along the length direction of the optical fiber, when the dual-core optical fiber 1 is not bent, the position interval of the two fiber gratings 4 along the length direction of the optical fiber determines the channel number and the channel interval of the comb spectrum; when bending along the plane of the two cores 3, the central wavelength of each channel of the output comb spectrum can be tuned.

Specifically, when the dual-core optical fiber 1 is not bent, the phase shift amount of the two reflected signals is determined only by the relative distance between the fiber grating 401 and the fiber grating 402, the reflection spectrum (the output of the first fiber core 301) thereof is a fixed comb spectrum, and the passband wavelength position and the comb spectrum envelope bandwidth thereof are determined by the relative positions of the fiber grating 401 and the fiber grating 402. When bending in the direction of the plane of the two cores 3, one core 3 is tensile strained and the other core 3 is compressive strained, since the two cores 3 are located on either side of the neutral axis of the fiber. The definition of strain refers to the ratio of the stretched or extruded length to the original length. So that the length of one core 3 is elongated and the length of the other core 3 is compressed to be smaller. At this time, the lengths of the two fiber cores are relatively changed to cause the optical path difference of the two optical signals, and the bending also causes the change of the refractive index, so that the phase shift amount of the reflected signals in the two fiber cores 3 is changed along with the change of the refractive index, and at this time, the transmission spectrum of the Michelson interferometer type is comb-shaped filtering response. The signal spacing of the comb spectrum (alternatively referred to as the free spectral range FSR) is proportional to the degree of bending of the fiber 3, and by varying the degree of bending of the fiber 3, comb filters of different signal spacing can be realized.

Preferably, in an exemplary embodiment, the fiber grating 4 is a uniform Bragg fiber grating or a linearly chirped fiber grating.

The uniform Fiber Bragg Grating (FBG) is a Fiber Bragg Grating in which the variation range or the variation period of the refractive index of the core of the Fiber is kept constant along the axial direction of the Fiber. The period of the refractive index variation of the uniform fiber Bragg grating is generally of the order of 0.1um, the reflection bandwidth is narrow, generally less than 1nm, and the shape of the reflection spectrum is Gaussian. The Linear Chirped Fiber Grating (LCFG) is a Fiber Grating formed by Linearly and gradually increasing (decreasing) the variation amplitude or the variation period of the refractive index of the Fiber core along the axial direction of the Fiber. Because the linear chirped fiber grating can reflect incident light with different wavelengths at different positions in the axial direction, the reflection spectrum of the linear chirped fiber grating is wide. The linear chirped fiber grating typically has a reflection spectral bandwidth of up to 10nm and a flat response within the passband.

More preferably, in an exemplary embodiment, the tapered coupler 4 is a 3dB coupler (typically 50: 50 split ratio).

Preferably, in an exemplary embodiment, the non-tapered coupler 2 portions of the cores 3 are all parallel to each other, and the grating plane 4 coincides with the plane formed by the first and second cores 301, 302.

With the same inventive concept, based on any of the above exemplary embodiments of the fiber-integrated tunable optical comb filter, in another exemplary embodiment of the present invention, there is provided a method for using the fiber-integrated tunable optical comb filter, including the following steps:

an optical signal input from the first fiber core 301 passes through the tapered coupler 2 and then outputs two paths of signals from an a1 port and an a2 port, the a1 port is one end of the tapered coupler 301 close to the fiber grating 4 side, the a2 port is the other end of the tapered coupler 2 close to the fiber grating 4 side, the a1 port is located on the first fiber core 301, and the a2 port is located on the second fiber core 302;

when the two optical signals pass through the first fiber bragg grating 401 and the second fiber bragg grating 402 respectively, the optical signals are reflected back, and interference is generated at the conical coupler 2 after the optical signals pass through the original path;

at this point, an interference signal will be output from the first core 301.

Since this content has already been explained in the course of the description of an exemplary embodiment of a fiber-integrated tunable optical comb filter, it is not repeated here.

With the same inventive concept, based on the above exemplary embodiment of any one of the fiber-integrated tunable optical comb filters, a further exemplary embodiment of the present invention provides an optical system, as shown in fig. 3, including:

the fiber-integrated tunable optical comb filter;

the single-mode fiber 5 is arranged on one side, away from the fiber grating 4, of the tapered coupler 2 and is connected with the first fiber core 301;

and an incident port of the optical circulator 6 is connected with the single-mode optical fiber 5.

Specifically, as shown in fig. 3, an optical signal input from port No. 1 of the optical circulator 6 is output from port No. 2 of the optical circulator 7, and then enters the tunable optical comb filter based on the fiber integration of the two-core fiber 1 from the first fiber core 301 along the forward direction of the fiber through the single-mode fiber 5, and the optical signal is reflected back from the first fiber core 301 along the reverse direction of the fiber after being reflected by the tunable optical comb filter based on the fiber integration. Next, the optical signal reflected from the first core 301 passes through the single-mode fiber 5, is input from the port No. 2 of the optical circulator 6, passes through the optical circulator 6, and is output from the port No. 3 of the optical circulator 6.

Specifically, in the present exemplary embodiment, both the first core 301 and the second core 302 may serve as input and reflection ports, and when the single-mode fiber 5 is fusion-spliced with the first core 301 of the two-core fiber 1, the first core 301 serves as an input port and also serves as a reflection port, a reflection signal is extracted from the first core 301; accordingly, when the single-mode optical fiber 5 is fusion-spliced with the second core 302 of the two-core optical fiber 1, the second core 302 serves as a reflection port and also serves as an input port, and a reflection signal is extracted from the first core 302.

In addition, the fusion of the single mode fiber 5 and the two-core fiber 1 is prepared by a fusion splicer, and the single mode fiber and one of the fiber cores 3 of the two-core fiber 1 are subjected to core-to-core fusion splicing by a manual mode of the fusion splicer.

Since the fiber-integrated dimmable comb filter of the foregoing exemplary embodiment is constructed using the two-core optical fiber, an optical system using the fiber-integrated dimmable comb filter is provided, and when the fiber-integrated dimmable comb filter constructed using the two-core optical fiber 1 of the present exemplary embodiment is adopted, the fiber-integrated dimmable comb filter has the characteristics of the fiber-integrated dimmable comb filter itself, and is convenient to integrate with other functional devices, and has high stability, so that the purpose of reducing the volume of the optical system is achieved, and certain requirements are met.

Another exemplary embodiment of the present invention provides a method for manufacturing a fiber-integrated tunable optical comb filter, as shown in fig. 4, including the following steps:

constructing a tapered coupler 2 on a dual-core optical fiber 1 in a fused biconical taper mode, wherein the dual-core optical fiber 1 comprises a first fiber core 301 and a second fiber core 302 which are symmetrically distributed on two sides of a neutral axis of the optical fiber, and the tapered coupler 2 is a 3dB coupler;

non-inclined fiber gratings 4 with consistent parameters are respectively inscribed on the same sides of the first fiber core 301 and the second fiber core 302 relative to the tapered coupler 2, and the two fiber gratings 4 are arranged at different positions along the length direction of the optical fiber.

The fusion splicer is a known optical fiber fusion splicing technology, and the working principle is that a high-voltage electric arc is utilized to melt the sections of two optical fibers and a high-precision motion mechanism is used for gently pushing the two optical fibers to fuse the two optical fibers into one, so that the coupling of an optical fiber mode field is realized. In the present exemplary embodiment, the tapered coupler 2 (preferably, a 3dB coupler) is prepared by a fused biconical taper method. In the preparation process, a position of the double-core optical fiber 1 close to a fusion point for a certain distance needs to be stripped with a coating layer of about 1cm, then a bare fiber part is aligned to a fire head position to be fused and tapered on an optical fiber tapering machine clamp, meanwhile, the coupling degree of two fiber cores 3 of the double-core optical fiber 1 is judged by monitoring the optical power change of a straight-through end in the tapering process, and tapering is stopped when the optical power of the straight-through end is reduced to be close to half of an initial value.

In addition, the writing step is also a well-known technique. Specifically, in the present exemplary embodiment, uniform Bragg fiber gratings or linearly chirped fiber gratings having uniform parameters are written in the two cores 3 at different positions in the fiber length direction using a phase mask technique or a femtosecond laser direct writing technique.

Specifically, when the fiber-integrated tunable optical comb filter in the present exemplary embodiment is used, two paths of signals are output from an a1 port and an a2 port respectively after an optical signal input from the first fiber core 301 passes through the tapered coupler 2 (when A3 dB coupler is used as the tapered coupler, the optical signal is uniformly distributed to the two fiber cores 3 after passing through the 3dB coupler), the a1 port is one end of the tapered coupler 301 close to the fiber grating 4 side, the a2 port is the other end of the tapered coupler 2 close to the fiber grating 4 side, the a1 port is located on the first fiber core 301, and the a2 port is located on the second fiber core 302;

when two optical signals respectively pass through the first fiber bragg grating 401 and the second fiber bragg grating 402, the optical signals are reflected back due to the same fiber bragg gratings 4 in the two fiber cores 3, and interference is generated at the conical coupler 2 after the optical signals return through the original path;

at this point, an interference signal will be output from the first core 301.

Similarly, when the dual-core optical fiber 1 is not bent, the phase shift amount of the two reflected signals is determined only by the relative distance between the fiber grating 401 and the fiber grating 402, the reflection spectrum (the output of the first fiber core 301) thereof is a fixed comb spectrum, and the passband wavelength position and the comb spectrum envelope bandwidth thereof are determined by the relative positions of the fiber grating 401 and the fiber grating 402. When bending in the direction of the plane of the two cores 3, one core 3 is tensile strained and the other core 3 is compressive strained, since the two cores 3 are located on either side of the neutral axis of the fiber. The definition of strain refers to the ratio of the stretched or extruded length to the original length. So that the length of one core 3 is elongated and the length of the other core 3 is compressed to be smaller. At this time, the lengths of the two fiber cores are relatively changed to cause the optical path difference of the two optical signals, and the bending also causes the change of the refractive index, so that the phase shift amount of the reflected signals in the two fiber cores 3 is changed along with the change of the refractive index, and at this time, the transmission spectrum of the Michelson interferometer type is comb-shaped filtering response. The signal spacing of the comb spectrum (alternatively referred to as the free spectral range FSR) is proportional to the degree of bending of the fiber 3, and by varying the degree of bending of the fiber 3, comb filters of different signal spacing can be realized.

The effect in this exemplary embodiment is the same as the inventive concept of the exemplary embodiment of the fiber-integrated tunable optical comb filter, and therefore, the description thereof is omitted.

Preferably, in an exemplary embodiment, the fiber grating 4 is a uniform Bragg fiber grating or a linearly chirped fiber grating.

More preferably, in an exemplary embodiment, when the dual-core optical fiber 1 is not bent, the position interval of the two fiber gratings 4 in the direction along the length of the optical fiber determines the channel number and the channel interval of the comb spectrum; when bending along the plane of the two cores 3, the central wavelength of each channel of the output comb spectrum can be tuned.

Preferably, in an exemplary embodiment, the non-tapered coupler 2 portions of the cores 3 are all parallel to each other, and the grating plane 4 coincides with the plane formed by the first and second cores 301, 302.

Still another exemplary embodiment of the present invention provides a manufacturing apparatus of a fiber-integrated tunable optical comb filter, having the same inventive concept as the manufacturing method, including:

the fusion splicer is used for constructing a tapered coupler 2 on a double-core optical fiber 1 in a fused biconical taper mode, the double-core optical fiber 1 comprises a first fiber core 301 and a second fiber core 302 which are symmetrically distributed on two sides of a neutral axis of the optical fiber, and the tapered coupler 2 is a 3dB coupler;

and the writing device is used for writing the non-inclined fiber gratings 4 with consistent parameters on the same side of the first fiber core 301 and the second fiber core 302 relative to the tapered coupler 2 respectively, and the two fiber gratings 4 are arranged at different positions along the length direction of the optical fiber.

Specifically, when the fiber-integrated tunable optical comb filter in the present exemplary embodiment is used, two paths of signals are output from an a1 port and an a2 port respectively after an optical signal input from the first fiber core 301 passes through the tapered coupler 2 (when A3 dB coupler is used as the tapered coupler, the optical signal is uniformly distributed to the two fiber cores 3 after passing through the 3dB coupler), the a1 port is one end of the tapered coupler 301 close to the fiber grating 4 side, the a2 port is the other end of the tapered coupler 2 close to the fiber grating 4 side, the a1 port is located on the first fiber core 301, and the a2 port is located on the second fiber core 302;

when two optical signals respectively pass through the first fiber bragg grating 401 and the second fiber bragg grating 402, the optical signals are reflected back due to the same fiber bragg gratings 4 in the two fiber cores 3, and interference is generated at the conical coupler 2 after the optical signals return through the original path;

at this point, an interference signal will be output from the first core 301.

Similarly, when the dual-core optical fiber 1 is not bent, the phase shift amount of the two reflected signals is determined only by the relative distance between the fiber grating 401 and the fiber grating 402, the reflection spectrum (the output of the first fiber core 301) thereof is a fixed comb spectrum, and the passband wavelength position and the comb spectrum envelope bandwidth thereof are determined by the relative positions of the fiber grating 401 and the fiber grating 402. When bending in the direction of the plane of the two cores 3, one core 3 is tensile strained and the other core 3 is compressive strained, since the two cores 3 are located on either side of the neutral axis of the fiber. The definition of strain refers to the ratio of the stretched or extruded length to the original length. So that the length of one core 3 is elongated and the length of the other core 3 is compressed to be smaller. At this time, the lengths of the two fiber cores are relatively changed to cause the optical path difference of the two optical signals, and the bending also causes the change of the refractive index, so that the phase shift amount of the reflected signals in the two fiber cores 3 is changed along with the change of the refractive index, and at this time, the transmission spectrum of the Michelson interferometer type is comb-shaped filtering response. The signal spacing of the comb spectrum (alternatively referred to as the free spectral range FSR) is proportional to the degree of bending of the fiber 3, and by varying the degree of bending of the fiber 3, comb filters of different signal spacing can be realized.

It should be noted that the effect in this exemplary embodiment is the same as the inventive concept of the exemplary embodiment of the fiber-integrated tunable optical comb filter, and therefore, the detailed description is omitted.

Preferably, in an exemplary embodiment, the fiber grating 4 is a uniform Bragg fiber grating or a linearly chirped fiber grating.

More preferably, in an exemplary embodiment, when the dual-core optical fiber 1 is not bent, the position interval of the two fiber gratings 4 in the direction along the length of the optical fiber determines the channel number and the channel interval of the comb spectrum; when bending along the plane of the two cores 3, the central wavelength of each channel of the output comb spectrum can be tuned.

Preferably, in an exemplary embodiment, the non-tapered coupler 2 portions of the cores 3 are all parallel to each other, and the grating plane 4 coincides with the plane formed by the first and second cores 301, 302.

It is to be understood that the above-described embodiments are illustrative only and not restrictive of the broad invention, and that various other modifications and changes in light thereof will be suggested to persons skilled in the art based upon the above teachings. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.